Vice President Kamala Harris is the presumptive Democratic presidential nominee. But can she win the presidency?

Due to the wonders of the Electoral College system, the answer depends on how she will do in a limited number of swing states.

In 2020, seven states had their presidential winner determined by less than 3 percentage points: Michigan, Wisconsin, Pennsylvania, Nevada, Arizona, Georgia, and North Carolina. Joe Biden won the first six out of those seven, so he won the White House.

When President Biden was still in the race, polling was looking grim for him in all these states. Commentators speculated that North Carolina, Arizona, Georgia, and perhaps even Nevada were out of reach for him.

Biden’s best path to victory, it was believed, was to hold strong in the Rust Belt trio of Michigan, Wisconsin, and Pennsylvania. Those three swing states, plus the traditionally Democratic states and a single electoral vote from Nebraska’s Second Congressional District, would have given Biden 270 electoral votes — the bare minimum he needed to win.

But Biden’s best path may not be Harris’s. There’s an optimist’s case that that’s good news for her — and a pessimist’s possibility that it’s a real problem.

The pessimistic case is that some suspect Harris may do worse among Rust Belt working-class whites than “Joe from Scranton” did — making states like Wisconsin and Pennsylvania a tougher reach for her.

The optimistic case is that perhaps Harris will do better than Biden among nonwhite voters — putting states with particularly large Black populations (Georgia and North Carolina) or Hispanic populations (Arizona and Nevada) back into contention.

Some initial poll results on how Harris does in swing states have trickled in since Biden dropped out, though given the recent upheaval in the contest, it’s not clear how much to make of them. But here’s how the swing state math stacks up.

In 2020, Biden won the national popular vote by 4.5 percentage points, but the contest for an Electoral College majority was much closer. Biden stacked up 19 safe Democratic states, the District of Columbia, and Nebraska’s Second District.

But he got over the top by triumphing narrowly in six of the seven swing states listed above. Here is his margin of victory in each:

Trump, meanwhile, won just one of the closest swing states:

Trump also won by 3.4 percent in Florida, which most analysts now believe should be considered a red-leaning state rather than a swing state.

The Biden-Trump rematch was set to focus on the same lineup of swing states, in about the same order of competitiveness as last time. However, one change is that many polls suggested that Nevada (a state Trump lost in 2016 and 2020) has since moved more to the right.

Now, Harris’s selection could scramble the map more. “Kamala Harris is doing SIGNIFICANTLY better than Joe Biden is among Black and Hispanic voters,” CNN polling analyst Harry Enten wrote on X, adding: “while Biden had really one path to win the electoral college, Harris has multiple. Specifically, she can win in the Sun Belt (AZ, GA, NC, & NV).”

Currently, the evidence that might happen is strongest in Georgia, where 33 percent of the population is Black and where there is polling showing Harris-Trump is a much closer race than Biden-Trump was. A Landmark Communications poll showed Harris down 1 point, and an Emerson College poll showed her down 2 points. (Biden was trailing by about 4 points on average when he dropped out of the race.)

North Carolina is more of a reach, considering Trump won it twice, but it was close in 2020 and the state is 21 percent Black. So perhaps Harris could make the state competitive — though it’s worth remembering that she hasn’t led a nationwide ticket yet, so we don’t yet truly know just how well she’ll do among Black voters when she’s the nominee rather than Biden’s running mate.

For Nevada and Arizona, the question is more about Hispanic voters, who make up more than 20 percent of the electorate in each state. Democrats have won Nevada in the past four presidential cycles, but it’s drifted right a bit in recent years. Arizona, meanwhile, is a traditionally Republican state that Democrats have had surprising success in in the past few cycles.

The Rust Belt power trio of Michigan, Wisconsin, and Pennsylvania famously determined the outcomes of both the 2016 and 2020 elections, by first swinging toward Trump and then to Biden.

If Harris wins all three again (as well as that Nebraska Second District vote), she wins the presidency. But what if she doesn’t win all three?

Another way to think about this is: If she loses one or more of the Rust Belt trio, what would she have to do to make up for that in the other four swing states (Georgia, North Carolina, Nevada, and Arizona)?

You can break down the scenarios in a few different ways, but here are a few:

1) If Harris loses all three of Wisconsin, Michigan, and Pennsylvania: She has a chance of still winning, but there’s no more room for error, and it relies on a big swing of both Black and Hispanic voters to her side. She would have to win all four of Georgia, North Carolina, Nevada, and Arizona — that would give her 275 electoral votes. This is easier said than done — Trump won North Carolina twice and he only lost Georgia and Arizona in 2020 by the slimmest of margins.

2) If Harris wins Michigan, but loses Wisconsin and Pennsylvania: The trio won’t necessarily move together. Biden did slightly better in Michigan than in the other two Rust Belt states in 2020, it has a larger Black population, and perhaps Harris could win back voters alienated by the Gaza war.

If she secures Michigan’s 15 electoral votes, Harris would have two paths. Winning both Georgia and North Carolina would be enough to put her over the top. Alternatively, winning one of those two plus both Nevada and Arizona would do it.

3) If Harris wins Michigan and Pennsylvania, but loses Wisconsin: Adding Pennsylvania would put her close — at 260 electoral votes. She would only need to win one of Georgia, North Carolina, or Arizona to put her over the top. (Nevada’s electoral vote haul is too small to get her there.)

This helps make it clear why Pennsylvania Gov. Josh Shapiro has emerged as a leading vice presidential contender — his state’s 19 electoral votes are extremely important to the electoral math, more so than, say, Arizona’s 11.

For now, all of this is speculative, since national voters have barely gotten a chance to make up their minds what they think of Harris since she became the presumptive nominee. She will have months to campaign in swing states to try to make her case — and the Trump campaign will also have months to try and make the case against her.

But the electoral math is already enough to show that, while her chances of victory may not utterly hinge on the Rust Belt states, her options are slim if she loses them.