Republicans made almost universal gains in mail voting during the 2024 election, eroding a key Democratic advantage in nearly every state that tracks party registration, according to a data analysis by The New York Times.

The Republican rise in the use of mail voting was almost always accompanied by a drop in registered Democrats casting a mail ballot, allowing Republicans to make significant inroads in battleground states such as Pennsylvania, red states such as Florida and blue states such as Connecticut.

The turnaround was remarkable given Republicans’ yearslong skepticism toward mail voting, fueled by President-elect Donald Trump’s false claims about fraud. The method was once widely embraced by Republicans in Southern and rural states but fell out of favor during and after the 2020 election as Trump and his allies argued that the only safe way to vote was in person on Election Day.

Making up ground in mail voting was a critical goal for Republicans heading into last year’s election, as GOP strategists worried that the party had created an opening for Democrats. Election experts in both parties have long believed that it is best to bank votes early, shrinking the universe of voters to target on Election Day and limiting the effects of bad weather or other unforeseen circumstances on turnout.

Trump, apparently cognizant of the Republican warnings, softened his stance in the final months of the 2024 election but still declared that he wanted “single-day voting.”

Coupled with a Republican surge in early in-person voting, the GOP improvement in mail voting cut heavily into what had been a major strategic advantage for Democrats. The development is yet another warning sign for the Democratic Party as it debates its failures and looks to the 2026 midterm elections. With dwindling structural advantages in addition to a fraying coalition, Democrats will need to improve their Election Day get-out-the-vote efforts, particularly among low-frequency voters.

Democrats still enjoy an overall advantage in mail voting in many states, including Pennsylvania and New Mexico, even with the Republican improvements. And the conservative support for mail voting could prove to be fragile. How Trump talks about mail voting over the next two years could decide whether Republicans keep up their 2024 momentum.

“If he blesses a certain way of voting, you’re going to see his followers and supporters embrace that,” said Michael McDonald, a prominent elections scholar and a professor of politics at the University of Florida. “It’s really remarkable, from the perspective of being a political scientist, that you would have a political figure say something and it would have that much effect on his supporters.”

Pennsylvania, widely seen as the most important presidential battleground, had one of the greatest swings in mail voting.

Its share of mail voters who were registered Republicans jumped to 33% in 2024 from 24% in 2020, according to data from the Election Lab at the University of Florida, while Democrats dropped to 56% of the mail-voting electorate in 2024 after registering 65% in 2020. (Post-election analyses focus on voters’ party registration because who they voted for remains secret.)

Because Pennsylvania does not have early in-person polling sites, it was clear to Republicans in the state that making up margins in mail voting would be essential for Trump and David McCormick, a Republican who ended up narrowly unseating the state’s senior senator, Bob Casey, a Democrat.

“Everyone knew we had a problem when you looked at the mail-in vote registration numbers,” said Andy Reilly, a member of the Republican National Committee from Pennsylvania. The breakdown, he added, was “70% Democrat, (22%) Republican and the rest independent, and we just couldn’t overcome that, particularly in ’22.”

That prompted Republicans to begin a multifaceted campaign of messaging, fundraising and field operations to right the ship, spearheaded by McCormick.

The first challenge: persuading Republican voters to trust mail voting.

“With Dave’s leadership, we ended up doing focus groups, and the three things that we thought that could get Republican voters to use mail-in ballots were, No. 1, Trump saying it’s OK,” Reilly said. “No. 2, convincing them that the military had been voting in this way forever. And No. 3, showing them that you can actually track your vote and it would count.”

Trump, for his part, sent mixed signals. In the early months of his candidacy, in 2023, he castigated mail voting and said he wanted “single-day voting,” a message many Republican voters took as a call to vote on Election Day.

But some of Trump’s allies began to encourage him to change his tune, at least somewhat.

“I worked hard to, you know, along with some other people, to get him to endorse it, and he did,” said Jim Worthington, a Republican donor and activist in Pennsylvania. “And that was key.”

By summer, Trump was encouraging voters to cast early ballots, including by mail, in a video message that was played at rallies and at the Republican National Convention in Milwaukee.

His different approach, however, was only part of the equation.

Republicans also needed to build a vote-by-mail operation essentially from scratch. Their effort in Pennsylvania began with a super political action committee founded by McCormick well before he announced his candidacy for the Senate, and eventually grew to include numerous groups, including the Sentinel Action Fund, Keystone Renewal PAC and the Republican State Leadership Committee. They spent millions of dollars to turn out Republican mail voters, often focusing on low-frequency voters. The McCormick and Trump campaigns also pushed Republicans to vote early.

Success trickled down the ballot. In the three most competitive congressional elections in the state, Republicans made double-digit gains in early voting that were similar to their statewide improvement. They won all three races by less than 2 percentage points.

Before Election Day, some Democrats speculated that the Republican gains in mail voting simply represented a shift in which high-frequency GOP voters had decided to cast early ballots, “cannibalizing” the party’s Election Day vote. But Republicans’ overall turnout edge proved to be real, and their improved early-voting numbers gave their campaigns an advantage.

“When we were looking at daily returns and saw huge gains in the Republican vote-by-mail share compared to previous election cycles, we knew we were on the right pathway to winning this election,” said Matt Gruda, who managed McCormick’s campaign. “We were seeing these gains not only among the most frequent voters but even more so also among the voters who rarely vote in our elections.”