DENVER (AP) - A majority of President Donald Trump’s supporters plan to cast their ballot on Election Day, while about half of Joe Biden’s backers plan to vote by mail, a sign of a growing partisan divide over how best to conduct elections in the United States.

Overall, 39% of registered voters say they will vote by mail, well above the 21% who say they normally do so, according to a new poll from The Associated Press-NORC Center for Public Affairs Research. The rise is skewed toward backers of the former vice president, 53% of whom plan to vote by mail. Fifty-seven percent of Trump’s supporters say they’ll vote in person on Nov. 3.

Fifty-four percent of voters say they will vote before polls open on Election Day. In 2016, roughly 42% of voters did so.

Trump for months has denigrated mail voting, and Democrats have expressed concern about postal delays that could keep such ballots from being counted. The poll finds ebbing enthusiasm for mail voting: Only 28% of Americans say they would favor their state holding elections exclusively by mail, down from the 40% who said so in April as the coronavirus pandemic was first spreading in the U.S. and before Trump launched his anti-mail campaign.

Support for states allowing voters to cast an absentee ballot without requiring a reason is higher, but also down since April, from 56% to 47%.

Sherry Santiago, 55, of Palm Bay, Florida, is disabled and cannot drive. The Democrat said she almost lost her chance to vote in 2016 because she couldn’t get a lift to the polling place and she’s happy to sign up for a mail-in ballot this year.

“I don’t want to take a chance of missing it,” Santiago said of the election. “I have total confidence in voting by mail. I don’t worry there will be a problem.”

Traditionally, voting by mail has not been a partisan issue.

Until recently, Republicans were more likely to do so than Democrats, because older voters have tended to vote by mail more often than younger voters.

The Centers for Disease Control and Prevention recommended earlier this year voting by mail as an alternative to face-to-face interactions at polling places, which could pose a risk of coronavirus infection. States have scrambled to adjust to an expected surge in advance voting, with nearly three dozen changing their mail or absentee voting rules in response to the pandemic.

The president has since tried to fan skepticism of mail voting, baselessly claiming that its widespread use will lead to fraud.

Trump warned that mail voting could lead to so many people voting that “you’d never have a Republican elected in this country again.”

He condemned on Thursday the plan in 10 states to proactively send mail-in ballots to registered voters, claiming without evidence it means the result of November’s election would never be accurately determined.

Studies of past elections have shown voter fraud to be exceedingly rare. In the five states that regularly send ballots to all voters, there have been no major cases of fraud or difficulty counting the votes.

The poll found that 33% of Democrats, but just 12% of Republicans, favor mail-only elections.

That’s a decline across the board from April, when 47% of Democrats and 29% of Republicans backed the idea. Seventy-two percent of Democrats, but just 25% of Republicans, favor no-excuse absentee voting.

In swing states like Florida, North Carolina and Pennsylvania, Democrats have far outpaced Republicans in requesting mail-in ballots so far this year.