The calendar says there’s more than a month until Election Day. But Pennsylvanians are already casting ballots now, and hundreds of thousands could be doing so within weeks. That creates new challenges for President Donald Trump, Joe Biden, and candidates across the state, as voting starts sooner — and spreads out longer — than usual.

With the coronavirus continuing to disrupt life, a big chunk of voters in Pennsylvania and other battleground states are expected to turn to mail voting, under which they can receive and send back ballots well ahead of Election Day, Nov. 3. A new state law makes it easier for anyone to do so, more than 2 million voters have already requested mail ballots, and ultimately about 3 million are expected to do so.

That has some Republicans worried that Trump has little time to make up ground in a critical swing state where Biden has a smaller but steady edge in polls. Some people may even vote before the first presidential debate Tuesday.

But the biggest impact, strategists in both parties said, could be on down-ballot races. Trump and Biden have the resources to handle a long period of advertising and get-out-the-vote efforts. Candidates for Congress or the state legislature have less money for a peak campaign season that could last weeks instead of days.

“Traditionally, there would be this sort of massive October push to make sure that people turn out on Election Day in November. That’s obviously very different right now,” said Adrianne Shropshire, executive director of BlackPAC, a grassroots group that engages progressive Black voters. “We consider ourselves to be in the [get-out-the-vote] phase right now.”

That means lesser-known candidates can’t save their election appeals and limited cash for the end, Shropshire said.

Voters “need to know in August, and they need to without a doubt know in September,” she said, “otherwise they’ll cast those ballots and skip really critical and important races because they won’t know who to vote for.”

That can strain challengers, who aren’t as well-known or well-funded as incumbents, said J.J. Balaban, a Democratic consultant in Philadelphia, who has also worked on races in Washington state, which votes almost entirely by mail.

He recalled when he helped Joe Sestak beat Arlen Specter in Pennsylvania’s 2010 Senate Democratic primary. Specter led big early, but Sestak caught him late in the race. If voters had cast their ballots early, Specter might have locked in some support that later slipped away.

As an example this year, Balaban pointed to Christina Finello, the Democrat running to unseat Republican U.S. Rep. Brian Fitzpatrick in Bucks County. She has far less campaign cash than Fitzpatrick. Such a challenger might normally save her big ad buys for the last 10 days of the race.

“She has to make a really tough choice between holding it until the end and missing a chunk of voters, or potentially communicating at such a light level for three weeks that she barely gets heard,” Balaban said.

» READ MORE: Voting has begun in Pennsylvania’s messy, unprecedented pandemic election

Whit Ayres, a Republican strategist who has worked on many races in Florida, where mail voting is prevalent, said it “complicates life enormously” for campaigns, “because you need to start advertising earlier, start getting out the vote earlier, but then you need to extend those efforts all the way up through Election Day.”

Trump and Biden are already tailoring their campaigns to the new reality.

In rolling out the $280 million Biden TV and digital campaign last week, Biden aide Patrick Bonsignore said the buy is “heavier in the summer and early fall than later on” compared with the past. And after pulling ads off the air when a new campaign manager took over, the Trump campaign planned to refocus its ads in states that start voting earliest, Politico reported.

But while early voting could shorten the window for a Trump comeback, strategists in both parties said people voting a month or two early are likely dedicated partisans who would pick their party’s candidate no matter what. In the primary election, only about one out of four ballots mailed in Philadelphia was returned more than a week before Election Day.

“The people who vote right away are the people who knew in the womb who they were going to vote for,” Balaban said, quoting a pollster he has worked with.

Still, if someone votes by mail, campaigns don’t have to worry about their failing to show up on Election Day because of a coronavirus surge, long lines, or a personal emergency. And the more people vote by mail, the shorter lines will be on Election Day, easing one potential obstacle in cities like Philadelphia.

For campaigns, early voting can also diminish the impact of late surprises that can sway undecided voters.

If recent primaries are any indication, the impact of the early voting is likely to be skewed, because far more Democrats are using mail voting than Republicans, as Trump attacks the method with false and exaggerated claims.

In Pennsylvania, more than one million Democrats used mail ballots in the June primary, compared with 397,000 Republicans. In other swing states like Florida and North Carolina, Democrats are far outpacing Republicans in requesting mail ballots.

» READ MORE: Women in Pittsburgh’s wealthy suburbs could help Biden beat Trump in Pa.

Despite the president’s rhetoric, the Republican National Committee and Pennsylvania GOP are encouraging voters to use mail ballots, and the Trump campaign says its strong staffing will eventually give it the edge in early voting. “You need to contact voters earlier, and it actually works to our advantage having the infrastructure we have,” said Ted Christian, a senior campaign adviser in Pennsylvania.

But other Republicans worry that Trump’s diatribes could hamper GOP turnout.

“It’s a concern that trashing the idea of mail voting is going to suppress Republican votes,” Ayres said. “Republicans could be leaving a whole lot of votes on the table if they discourage their own supporters from voting by mail.”

NextGen, a progressive group focused on voters aged 18 to 35, usually builds its major get-out-the-vote effort during the four days leading up to Election Day, said Larissa Sweitzer, the group’s Pennsylvania state director.

Now, it’s already reaching out to make sure young voters know about mail-in voting. The group texted more than 700,000 Pennsylvanians last week.

“It does expand the amount of time that we have to talk to voters,” Sweitzer said. “It’s our job, it’s our responsibility, to then retouch those voters. … Do you know where to return that ballot? Do you know when to return that ballot? … Did you sign your ballot?”

As the election goes on, widespread mail voting can help campaigns see what’s working, what isn’t, and who to target, since public records show who has requested a mail ballot — and who has returned one.

“You can really get a sense of who’s showing up, and that allows a campaign to start tailoring their message toward later voters who are maybe undecided,” said Christian Sinderman, a Democratic consultant from Seattle who also works on races in Oregon, another state that votes almost entirely by mail.

And campaigns can better target their phone calls and mailings, since they know who hasn’t voted yet.

“If you want to be left alone before Election Day,” Sinderman said, “send in your ballot early.”