Philadelphia voters will soon hear a familiar election-year sound at their front door: the rap-rap-rap of a Democratic official canvassing for support. But the message they hear might take them by surprise.

After a monthslong effort to get voters to embrace mail-in voting, Democrats in Philadelphia will push supporters to vote in person if they have not already requested a ballot.

The sudden shift in tactics in the biggest city in Pennsylvania, a critical swing state, reveals unease over President Trump’s war on mail-in voting and a rash of court rulings that are still altering the regulations that will govern how ballots are cast and counted in November.

“The only secure thing is to walk to the polls, put your mask on, bring some hand sanitizer — just go vote,” said Bob Brady, a former congressman and the chairman of the Philadelphia Democrats. “This president is going to do everything he can to fight any state, or any city that has an overwhelming vote against him — and we will have an overwhelming vote against him. And we’ll be in his cross hairs.”

Democrats nationally have not abandoned their efforts to vote by mail, largely because their electoral fortunes are wedded to the process. Democrats vastly outnumber Republicans in absentee ballot requests in key battleground states; in Pennsylvania, nearly 1.5 million Democrats have requested a mail-in ballot, three times the requests from Republicans. Since Wisconsin began mailing absentee ballots on Sept. 16, nearly all of the state’s counties that voted for Hillary Clinton in 2016 have returned ballots at a higher rate than counties that backed Mr. Trump.

Many state parties and officials continue to view voting by mail as essential amid the coronavirus pandemic. Joseph R. Biden Jr.’s campaign is still encouraging its supporters to have a plan to vote and to know their options, and that includes voting by mail.

But the change in Philadelphia indicates that some voters are becoming increasingly worried about placing completed ballots in the mail — and that election officials are adjusting accordingly.

As the president falsely claims that mail balloting is rife with fraud, and as the election system has been overtaxed by the vote-by-mail surge, voters across the country have been left to navigate a confusing process. Not only are the rules still being litigated, disinformation from both foreign and domestic sources is also cluttering their social media feeds.

Mr. Trump, knowing that lackluster turnout in Philadelphia could help him win the state, has sought to cast the city in a nefarious light and has suggested that officials there are working against him. “Bad things happen in Philadelphia,” he said at Tuesday night’s debate. On Thursday, the Trump campaign repeated that accusation in a lawsuit it filed against Philadelphia, protesting the decision by city officials to prohibit campaign representatives from watching people registering to vote or filling out mail-in ballots in election offices.

Democrats in Wisconsin said many voters were still requesting absentee ballots, but were increasingly worried about returning them through the mail.

In Madison, Wis., by far the state’s most Democratic stronghold, the city clerk’s office received so many phone calls from voters worried about the Postal Service that on Saturday it dispatched 1,000 poll workers to more than 200 city parks. Their job was to collect ballots in an event the city called “Democracy in the Park.”

“The volume was pretty incredible,” said Maribeth Witzel-Behl, the city clerk. “A lot of calls were coming in, voters saying, ‘I’ve got my ballot, I’ve got the envelope complete, but I am reluctant to put it in the mail.’”

Ms. Witzel-Behl, who attributed voter sentiment to “comments that have been made about voting by mail at the national level,” is planning another ballot-return event on Saturday, before the city’s 14 drop boxes are installed at municipal fire stations next week.

A grass-roots nonprofit group called #walkthevote has been organizing voting “parades” in a dozen states, including Michigan, Texas and Wisconsin. The events gather groups of voters to drop off their absentee ballots in person at elections offices or drop boxes.

ImageWorkers stuffed ballots that would be sent to voters in West Bloomfield Township, Mich.
Credit…Sylvia Jarrus for The New York Times

Kyra Harris Bolden, a Michigan state representative from the Detroit suburbs, is organizing half-mile marches on Sundays to deposit ballots in a drop box at City Hall in Southfield, Mich. For those who can’t get to a drop box, Ms. Bolden said, she is encouraging them to return mailed absentee ballots within 48 hours of receiving them.

“There are just some people who want to see their ballot go into the machine,” she said. “We’re just making people aware of all of their options. We want people to feel comfortable putting ballots in the mail, but you can be sure if you drop it off in the drop box.”

William Velchoff of Georgetown, Texas, was among the Democrats who said they planned to vote in person.

“I think Trump and the Republicans in general are trying to screw up mail-in voting,” said Mr. Velchoff, a retired manufacturing engineer who worked in the oil industry. “They’ve given every indication that they’re going to do what they can to throw out mail-in votes.”

The debate over how much to shift away from mail voting comes as Philadelphia Democrats are planning to resume in-person campaigning this weekend, though still safely and socially distanced, after months of digital outreach and phone banking to stay safe during the pandemic. On Thursday, the Biden campaign said it would begin door-to-door canvassing in battleground states.

For some Democratic officials, the push on mail voting is a way to increase their success in the margins, where close states are likely to be decided. Ben Bright, the chairman of the Democratic Party of Washington County, Pa., said he encouraged “low-propensity voters” — those who don’t regularly cast a ballot — to vote by mail. But for “super-voters,” or those who participate in every election, he advised voting in person. That way they will avoid any mistakes that can cause an absentee ballot to be rejected.

“Our thought has always been that if we get 1,000 Democrats to vote by mail that wouldn’t have voted otherwise, and we lose 10 percent due to mistakes, we still gained 900 votes,” Mr. Bright said. “But if 1,000 super-voters decide to vote by mail, and 10 percent of their votes are lost due to mistakes, then we’ve lost 100 votes we otherwise should have had.”

The worries about honest mistakes are part of the reasoning behind the shift in Philadelphia. Officials there recently warned that a decision from the State Supreme Court instructing officials to discard so-called “naked ballots” — those that arrive without a secrecy envelope — could risk up to 40,000 votes in the city. That’s a significant amount in a Democratic city where Mr. Biden needs to run up the margins to have a chance at winning back Pennsylvania.

Philadelphia Democrats are not planning to wholly abandon voting by mail; of the 300,000 voters in the city who requested an absentee ballot, roughly 250,000 came from registered Democrats, according to data provided by the Pennsylvania secretary of state’s office.

But nearby, the Bucks County Democratic Committee, which represents one of the city’s densest suburbs, is not encouraging any change.

“We urge people not to give into the scare tactics being used by the Trump campaign and G.O.P.,” said Alex Porco, the committee’s executive director, adding that “ultimately voting by mail is safe, secure and convenient.”

Marc Morial, the president of the National Urban League, said he knew that some people didn’t want to vote by mail. “I hear from lots of people who do not trust the mail,” said Mr. Morial, a former New Orleans mayor. “If you do not trust the mail, vote another way.”

But the Urban League is advocating what Mr. Morial calls “optionality.”

“We would be cutting off our nose to spite our face if we were spooked into saying to people, ‘Don’t vote by mail,’” he said. “We could end up disenfranchising millions.”


Credit…Lauren Justice for The New York Times

In Wisconsin, Republicans have sought to block officials from conducting mass ballot collections. The Republican leaders of the State Assembly and State Senate both objected to Madison’s “Democracy in the Park” events, and the Republican Party of Wisconsin sent letters to the Milwaukee Brewers and Milwaukee Bucks franchises warning them against having team mascots — Bango, the Bucks’ deer-like mascot, Bernie Brewer, and the Brewers’ five racing sausages — appear at early-voting sites.

Wisconsin is not the only state where Republicans are trying to limit the number of drop-off locations. In Texas, Gov. Greg Abbott issued a proclamation on Thursday restricting counties to just one ballot drop-off site each, requiring some of the state’s largest and most Democratic counties to close facilities on Friday.

Chris Walton, the Democratic Party chairman of Milwaukee County, said Democrats there were wary about putting their ballots in the mail — the county lags well below the state average in its rate of absentee ballots returned. He has pushed voters to return ballots at public libraries and city halls that have drop boxes.

“We just have to get better,” Mr. Walton said. “There’s newfangled technology like the light bulb, it’s scary at first. And now we have a new light bulb, and that’s scary too.”

Stephanie Saul and Trip Gabriel contributed reporting.