Vice President Kamala Harris chose Minnesota Gov. Tim Walz as her running mate Tuesday.

Walz’s selection came as something of a surprise. For much of last week, betting markets had given Pennsylvania Gov. Josh Shapiro a more than 60 percent chance of joining the Democratic ticket. In opting for Walz instead, Harris defied the conventional wisdom among Democratic consultants, who had broadly favored Shapiro. And on Tuesday morning, some close to the Trump campaign told CNN that they were “breathing a sigh of relief” that the Democratic nominee had not tapped the popular Pennsylvania governor.

The wisdom of choosing Walz over Shapiro is therefore bound to be widely debated. And each side in that argument has reasonable points. Here is a rundown of the case for, and against, believing that Harris’s first major decision as leader of her party was a mistake.

The case for picking Shapiro over Walz is twofold:

Right now, Harris is polling a bit worse in Pennsylvania than in the other key Rust Belt battlegrounds. The likely Democratic nominee trails former President Donald Trump by 1.2 points there, while tying Trump in Wisconsin, and leading him by 2 points in Michigan, according to RealClearPolitics’s polling averages. Close the gap in Pennsylvania, and Harris will be in striking distance of sweeping the three Midwestern swing states, which could be sufficient to win her the White House.

Further, Pennsylvania holds four more Electoral College votes than Michigan and nine more than Wisconsin. As long as Democrats win Pennsylvania, they can lose both of those states and still retain some other plausible routes to victory. With Pennsylvania in her corner, Harris could lose Nevada, Michigan, and Wisconsin — and still get just over 270 Electoral College votes by taking Georgia and Arizona.

Shapiro could plausibly have helped Harris pull past Trump in Pennsylvania. In some recent polls, the governor’s approval in the state sits at 60 percent. Last month, a Public Policy Polling survey found Trump leading Harris in Pennsylvania by 2 points — but when the same respondents were presented with a choice between a Harris-Shapiro ticket and one featuring Trump and Ohio Sen. J.D. Vance, the former led by 1 point.

Although winning Pennsylvania is important, it is obviously not sufficient. But there is some reason to think that Shapiro could have helped Harris in other pivotal states.

Harris’s greatest political liability may be the widespread perception that she is very left-wing. The Democratic nominee hails from one of the most liberal parts of one of America’s most liberal states. During her time in the Senate, she racked up one of Congress’s most progressive voting records. And in her ill-fated primary campaign in 2020, Harris embraced several very left-wing policies, such as the decriminalization of border crossing, a fracking ban, and Medicare-for-all. Republicans are already trying to use these positions against her in attack ads.

Harris has tried to neutralize this vulnerability by disavowing her past positions, championing bipartisan border security legislation, and spotlighting her career as a moderate, “smart on crime” prosecutor.

Shapiro’s selection could have aided this rebranding effort. The Pennsylvania governor has a well-earned reputation for moderation. Since Republicans control Pennsylvania’s Senate, Shapiro has only ever enacted bipartisan legislation. He is therefore associated with various anodyne, broadly appealing initiatives, such as establishing universal, free public school breakfasts, removing college degree requirements for many public sector jobs, and spearheading the rapid reconstruction of a collapsed stretch of I-95 in Philadelphia. As New York magazine’s Jonathan Chait notes, Shapiro has also proven himself a deft communicator to those on the right side of the aisle. After a would-be assassin wounded Trump and killed one of his most prominent local supporters at a rally in Butler, Pennsylvania, Shapiro delivered a stirring eulogy for the deceased, a firefighter named Corey Comperatore. His tribute to the civic pride and familial devotion of a political adversary had wide resonance, and may be partly responsible for his strong approval in recent polls.

Shapiro’s credibility with voters who dislike Trump — but distrust progressives — is arguably enhanced by his high-profile criticism of pro-Palestinian campus occupations, and the Democratic left’s consequent opposition to his candidacy for vice president.

To be sure, Walz is scarcely an inveterate progressive. For more than a decade, he represented a Republican-leaning, rural House district and assembled the voting record to prove it. During his last session in Congress, Walz voted in line with the preferences of the conservative group Heritage Action 15 percent of the time, which was more than twice as often as the average House Democrat.

Nevertheless, as governor of Minnesota in 2023, Walz assembled an impressively vast and progressive governing agenda. Despite the fact that his party held the state senate by a single seat — which it had won by just 321 votes — they nevertheless managed to enshrine abortion rights, establish paid family and medical leave, restore the voting rights of ex-felons, invest $1 billion into affordable housing, impose background checks on private gun transfers, legalize recreational marijuana, create a refuge program for trans people denied gender-affirming care in other states, mandate that utilities go carbon-free by 2040, prohibit non-compete clauses in labor contracts, empanel a statewide board to set minimum labor standards for nursing-home workers, direct $2.58 billion into improved infrastructure, and increase taxes on corporations and high earners, among myriad other reforms.

Minnesota’s frenzy of progressive legislating caught the attention of progressives nationally. And when Harris named both Walz and Shapiro to her shortlist, left-wing groups and commentators began agitating for the former’s selection and against the latter’s.

For these reasons, Walz’s selection may abet a Republican narrative that Harris is a “dangerously liberal” figure in respect to the left, while Shapiro might have theoretically undercut that impression.

But none of that necessarily means that choosing Walz was a mistake. There are at least five arguments for favoring him over Shapiro:

• Walz balances the Democratic ticket in some ways that Shapiro wouldn’t have.

•The Minnesota governor has excelled in recent television appearances, coining a line of attack against the Republican ticket that subsequently went viral.

• In recent days, news reports surfaced a couple potentially damaging stories about Shapiro.

• Shapiro’s capacity to help Harris in Pennsylvania might be overstated.

• Shapiro’s selection would have been more divisive within the Democratic coalition and could have jeopardized the spirit of enthusiasm and unity that has prevailed within the party since Biden stepped aside.

For reasons noted above, Walz does not balance the ticket ideologically as much as Shapiro might have. But he arguably balances it more than the Pennsylvania governor demographically. Unlike Harris and Shapiro (and Joe Biden, Barack Obama, Hillary Clinton, and Bill Clinton), Walz did not go to law school and did serve in the military.

He hails from a tiny town in rural Nebraska, and is an avid hunter and onetime high-school football coach. He therefore has deep roots in the small-town Midwest, an area of deepening weakness for the Democratic Party. In theory, this could render Walz a more effective messenger to swing voters in Wisconsin and Michigan than Shapiro, who was raised in eastern Pennsylvania and spent most of his life on the East Coast.

Granted, Walz did not perform especially well in rural Minnesota during his 2022 governor run. But during his long tenure in the House, he did unusually well in non-urban areas for a Democrat. Walz knows how to appeal to such voters. To the extent that the Harris campaign believes it needs to reassure voters who are moderate to conservative on some issues, Walz will surely be game to triangulate. Given progressives’ personal affection for and trust in Walz, it is possible that they may give a Harris-Walz ticket greater leeway for pragmatic repositioning than a Harris-Shapiro ticket would have enjoyed.

A presidential nominee’s running mate is her primary surrogate. And Walz proved himself an able attack dog in recent weeks. During a July 23 appearance by Walz on MSNBC’s “Morning Joe,” the governor lamented, “We do not like what has happened, when you can’t even go to Thanksgiving dinner with your uncle because you end up in some weird fight that is unnecessary … Well, it’s true. These guys are just weird.”

Democrats both online and off latched onto Walz’s message — that Trump’s GOP had developed a “weird” and off-putting political culture. One recent poll from a Democratic outfit suggests that this message broke through, with voters saying that the word “weird” better describes Republicans than Democrats by a 47 to 37 percent margin.

Separately, as reporters dug into Harris’s list of VP contenders in recent weeks, they surfaced more potentially damaging stories about Shapiro than about Walz. One of those stories was already well-known, but attained newfound prominence: A top Shapiro aide allegedly subjected one of his office’s employees to persistent sexual harassment last year. The governor’s office reached a $295,000 settlement with that employee. Shapiro insists that he had no knowledge of this misconduct until months after the events. Given how close Shapiro was to the aide in question — his secretary of legislative affairs, Mike Vereb — it is not irrational to worry whether that claim would have held up under journalistic scrutiny.

There is also the strange and tragic case of Ellen Greenberg. A 27-year-old resident of Philadelphia, Greenberg was found dead of 20 stab wounds in 2011. That case was initially ruled a homicide and then reclassified as a suicide. The seeming improbability of a person successfully stabbing themselves 20 times led both Greenberg’s family and the public writ large to find the police’s conclusion outrageous. Nevertheless, when Shapiro was Pennsylvania’s attorney general in 2019, his office upheld the city’s finding of suicide. Recently, the Pennsylvania Supreme Court agreed to take up the Greenbergs’ civil case against Philadelphia.

Walz is not wholly devoid of personal scandals; in 1995, he was arrested for driving while intoxicated. But his publicly known personal liabilities are less recent and potentially incendiary than Shapiro’s.

Historically, presidential candidates have not consistently performed better in their running mates’ home states. In a 2019 study, the political scientists Christopher J. Devine and Kyle Kopko used large-scale survey data to gauge whether voters who lived in a VP candidate’s home state were more likely to support that candidate’s party than other voters were, after controlling for all other relevant variables (e.g., partisanship, race, age, gender, income, etc.). They found no such effect. And this result was consistent with most other studies on the subject, which have found that vice presidential candidates do not reliably enjoy a “home state advantage.”

To be sure, there are real limitations to what such research can tell us. Neither party’s presidential nominees have actually tried putting a popular politician from a top-tier swing state onto the ticket in generations. To the contrary, both parties have made a habit of picking VP candidates from completely uncontested red or blue states. Thus, it’s possible that historical data is a poor guide to the actual consequences of elevating Shapiro.

Nevertheless, the fact remains that there is little empirical basis for certainty about Shapiro’s ability to substantially increase Democratic support in Pennsylvania. Political figures’ approval ratings can change dramatically when they join a presidential ticket. Hillary Clinton had a 65 percent approval rating as secretary of state. Not long into her 2016 presidential run, however, she became historically unpopular.

If Shapiro ceased to be an inoffensive bipartisan governor and became one of Donald Trump’s leading adversaries, his support with Pennsylvania Republicans could have crashed. Whether his standing with the state’s undecided voters would hold up is impossible to know in advance.

The second cause for concern about Shapiro’s nomination is its potential to inflame some of the Democratic Party’s internal divisions. Most conspicuously, his selection threatened to heighten the salience of intra-Democratic disputes over US policy toward Israel.

From one angle, Shapiro’s views on the Jewish state look indistinguishable from those of Walz and other mainstream Democrats. He supports the two-state solution and has called Israel’s Prime Minister Benjamin Netanyahu “one of the worst leaders of all time.” Meanwhile, Walz has voiced enthusiastic support of Israel and its right to defend itself, and once took a personal meeting with Netanyahu and posed for a photograph with him.

This has led some commentators to suggest that progressives’ unique antipathy for Shapiro is informed by antisemitism. Although this is surely true in some individual cases, there is a rational basis for pro-Palestinian Democrats to be particularly distrustful of the Pennsylvania governor.

Much of the debate over Shapiro’s posture on Israel-Palestine has focused on an interview he gave to CNN in April. During that conversation with anchor Jake Tapper, Shapiro drew an analogy between the most antisemitic, pro-Palestinian campus protestors and the KKK. Some progressives have suggested that Shapiro was comparing all pro-Palestine demonstrators to klansmen. And his defenders have rightly observed that this is false: Shapiro explicitly defended the legitimacy of peaceful dissent against Israel in the interview, and made clear that he was specifically denouncing those who engaged in the antisemitic harassment of Jewish students. And that is not substantially different from Walz’s own remarks on the subject.

Yet Shapiro’s hostility toward pro-Palestine advocacy is not limited to some stray remarks on cable news. In 2016, Pennsylvania enacted a law that forbade the state from contracting with businesses that boycott Israel. Many legal scholars consider this to be an unconstitutional abridgment of freedom of speech, as it requires the government to discriminate against business owners on the basis of their political activity.

Shapiro is an avid supporter of the legislation. And as Pennsylvania attorney general in 2021, he implored the state’s agencies to enforce the law against Ben & Jerry’s, after the ice cream company refused to license its product for sale in the West Bank. Given that Israel’s ongoing occupation of that territory is both a violation of international law and an obstacle to the creation of a Palestinian state, Shapiro’s enthusiasm for punishing an act of protest against that occupation may call his commitment to the two-state solution into question.

The percentage of voters who care deeply about the Israel-Palestine conflict — and believe the Democratic Party is excessively supportive of Israel — is not large. But this contingent is disproportionately influential on social media, and may thus indirectly color the impressions of less politically engaged younger voters.

For much of this year, progressive outrage over American complicity in the devastation of Gaza loomed large on the social media platforms X and TikTok. Following Harris’s replacement of Biden, such discourse was largely displaced by joyful memes highlighting the vice president’s relative youth and vigor. Shapiro’s selection threatened to dampen that mood shift.

Meanwhile, Shapiro’s support for publicly subsidizing private school attendance has earned him some opposition from the labor movement (public school teachers are typically unionized while private school ones are not). United Auto Workers President Shawn Fain expressed concern about Shapiro’s commitment to labor’s interests last Thursday.

Ultimately, Walz was a solid choice. He could plausibly help Harris ingratiate herself to Midwestern voters, enable her to moderate where necessary with only limited intra-party pushback, and, if all goes well, serve as an able governing partner.

Of course, if Democrats wake up on November 6 having narrowly lost Pennsylvania — and thus, the Electoral College — many will surely lament Harris’s failure to tap the popular governor of the most important battleground state.

Regardless, it will be very difficult for Walz to work out much worse than his GOP counterpart.