Both Vice President Kamala Harris and former President Donald Trump have been on a fundraising blitz in recent weeks.

Since President Joe Biden announced his decision to step aside as the Democratic nominee, Harris has raised over $310 million for her campaign, with 66 percent of donations coming from first-time contributors. The Democratic super PAC Future Forward also said it had received $150 million in commitments in the first 24 hours after Biden ended his campaign. And by 5 pm on Tuesday, Democrats raised more than $24 million through their ActBlue PAC after Harris announced that Minnesota Gov. Tim Walz would be her running mate. Big-money donors, such as co-founder Reid Hoffman and billionaire entrepreneur Mark Cuban, have come out to support her pick, suggesting that they may be writing more checks to her campaign.

All of that has largely erased Republicans’ fundraising advantage.

Trump was outraising Biden before the president dropped out of the race. In June (the month after he was convicted of 34 felonies), his campaign took home a $111.8 million haul, and the Republican National Committee had its strongest month of fundraising in years, bringing in $66 million. In the wake of both an assassination attempt against him and the spectacle of the Republican National Convention, Trump bested his June total, reportedly pulling in $137 million in July.

But how much will any of that money actually impact the results?

Presidential campaigns have long been expensive, but the money required to run a successful presidential campaign has ballooned since the Supreme Court’s 2010 ruling in Citizens United v. Federal Election Commission. That decision allowed corporations and outside groups to spend unlimited money on elections, often via super PACs that operate independently of a campaign. 2020 marked the most expensive presidential election in US history.

“Presidential elections are incredibly expensive — at this point, a billion-dollar enterprise,” said Dan Weiner, director of the Brennan Center for Justice’s elections and government program. “You need enough money to mount a viable campaign.”

That money goes toward supporting staffers and field offices across the country; ads across television, newspapers, radio, and social platforms; polling and research; as well as voter outreach through rallies, door-knocking, and more.

Both grassroots support and big donors are critical to funding a presidential campaign. Citizens United gave the wealthiest donors outsize influence. But grassroots donations are a sign of enthusiasm: They don’t necessarily translate 1-to-1 to votes, but they also function as a signal to big donors about which candidates are the most viable.

Both Harris and Trump will need to keep the money flowing, said Brendan Glavin, deputy director of research for OpenSecrets. While it’s not that early in the cycle — Trump has been campaigning since November 2022 — the most intense weeks of the election are yet to come. Now is when candidates typically travel more often to battleground states, hold more rallies, fine-tune their strategies through more frequent polling, and ramp up advertising and get-out-the-vote efforts.

While recent events have spiked voter enthusiasm in both parties, previous campaigns suggest the most lucrative days might be ahead. There are still 13 weeks until Election Day, and it was in the 10 weeks before the 2020 election that Biden brought in about 60 percent of his overall fundraising haul.

Money, however, isn’t everything. While the victor in presidential contests often has the fundraising edge, that isn’t always the case. Piles of cash ultimately can’t compensate for poor spending decisions or bad candidates.

Biden outspent Trump in 2020. But Hillary Clinton, the former Secretary of State and Democratic nominee in 2016, far outspent Trump yet still lost the election. Her campaign spent heavily in states she didn’t need to win, including Arizona, but neglected Rust Belt states that ultimately cost her the election.

And then there are the well-funded campaigns that never really got off the ground because of a weak candidate.

“Put lipstick on a pig, it’s still not going to be a good candidate,” said Ray La Raja, associate director of the UMass poll and a political science professor at the University of Massachusetts Amherst. “No amount of money is going to make a bad candidate really good.”

Take former New York City Mayor Michael Bloomberg’s four-month Democratic primary campaign in 2020 that cost him $1 billion of his own money. “In the end, primary voters did not respond to him,” Glavin said. “He had the money. He got his name out there. But he didn’t get the response.”

Campaigns like Clinton’s and Bloomberg’s show that money is only one piece of the puzzle. Research suggests that challengers benefit more from campaign spending than incumbents, and that for any candidate, early spending is more effective than late spending. Incumbents don’t benefit as much from campaign spending because voters often already know who they are and there isn’t as much room to change their minds about that. The research suggests that the more incumbents spend, the more likely they are to lose — the spending itself is usually a signal that they are in hot water.

Harris has some advantages of an incumbent in that she has Biden’s campaign apparatus behind her, but in other respects, she fits the profile of a challenger.

“That marginal dollar is worth more to a challenger. And she’s more in that role, because let’s face it: Most people don’t know what the vice president does,” La Raja said.

Harris is still introducing herself — and Walz as her new running mate — to the American public. She is newly in the spotlight and has a window to shape her image in a way that a typical candidate might not. Her campaign is therefore spending heavily on ads right now, dropping $50 million on paid media ahead of the Democratic National Convention in August.

“It’s a well-known dynamic in presidential races that you try to define your opponent early,” Weiner said. “I have no doubt that what the Harris campaign wants to do — and also part of the reason why it was so critical that they raise so much money so quickly — is to define her before the Trump campaign can define her.”

Americans may have somewhat forgotten what the Trump presidency was like, but as a former president, Trump is already fairly well-defined to voters and fits the profile of an incumbent more readily than a challenger. As a result, his strategy has been to leverage established recognition — and go on offense against Harris with a slate of attack ads.

But there are diminishing returns on ad spending, since the media gives presidential candidates so much free coverage. Trump may not have spent as much as Clinton in 2016, but he certainly benefited from the media limelight that year — and so did the media, which experienced a “Trump bump” in viewers and readers. This year, Trump has successfully fundraised off of big media events, like a conviction or the assassination attempt against him. So, too, has Harris after Biden dropped out.

Their fundraising — and electoral — success will likely depend on whether that momentum lasts. Also, at a certain point, “money has diminishing returns,” Weiner said. There are only so many ads a candidate can buy, doors they can knock on and rallies they can hold to make their best case to voters. Once a candidate and their positions are well-understood, they can only hope that voters prefer them.

“If you’ve raised enough money, raising even more money doesn’t help you that much,” he said.