JOHNSTOWN, Pa. (AP) — With Election Day just three weeks away, President Donald Trump and Democratic challenger Joe Biden concentrated Tuesday on battleground states both see as critical to clinching an Electoral College victory, tailoring their travel to best motivate voters who could cast potentially decisive ballots.

While Trump visited Pennsylvania, Biden hit Florida to court seniors, betting that a voting bloc that buoyed Trump four years ago has become disenchanted with the White House's handling of the coronavirus pandemic. It was Biden's third visit to the state in a month, after making targeted appeals to other communities, including veterans and Latinos.

To Trump, "you’re expendable, you're forgettable, you’re virtually nobody,” Biden said at a senior center in Pembroke Pines, about 20 miles (32 kilometers) from Fort Lauderdale.

The “only senior Donald Trump seems to care about" is himself, Biden added.

Tim Murtaugh, a spokesperson for Trump’s campaign, said in a statement that “Biden is playing politics with people’s lives over the virus.”

After frequently criticizing Trump for not doing enough to promote wearing masks to prevent the spread of the virus, Biden was wearing two masks, an N-95 underneath a blue surgical mask, as he deplaned in Florida. Later in the day, he switched to his normal mode of donning just one.

Introducing Biden in Pembroke Pines, Democratic Rep. Debbie Wasserman Schultz noted that “neither of these men will walk into the White House without the blessing of Florida seniors.”

“Much is made of the rise of the youth vote, and thank God for it," the Florida congresswoman said. "But it’s residents 65 or older who still swing elections in the Sunshine State.”

Biden also held a drive-in rally designed to promote voter mobilization in the heavily African American community of Miramar. His swing coincided with a $500,000 donation from billionaire former New York Mayor Mike Bloomberg to increase Democratic turnout in Miami-Dade County.

“I'm running as a proud Democrat, but I will govern as an American president,” Biden said to supporters blaring their horns as they listened from cars. “I'll work as hard for those who vote against me as those who vote for me."

Boarding Air Force One to fly to Pennsylvania, Biden's native state, Trump said he expects a large crowd. He wants to hammer home the claim that a Democratic administration could limit fracking in areas where the economy is heavily dependent on energy. Biden has proposed only barring new leases on federal land, a fraction of U.S. fracking operations.

Biden "has handed control to the socialists, Marxists and left-wing extremists,” Trump plans to say, according to excerpts released by the White House. “If he wins, the radical left will be running the country — they are addicted to power, and God help us if they get it.”

It's part of an effort to fire up a conservative base that Trump will have to turn out in droves to secure the 270 electoral votes needed to retain the White House. The president also campaigned in Sanford, Florida, on Monday and will head back to the state on Friday.

Campaign travel on both sides comes against the backdrop of a second day of Senate hearings to confirm Amy Coney Barrett to the Supreme Court. Trump and top Republicans see a swift confirmation just weeks after the death of liberal Justice Ruth Bader Ginsburg as a chance to energize conservatives. Trump mentioned those proceedings as he boarded his flight, saying, "Amy was doing incredibly well.”

Biden's campaign believes it can take the presidency without Florida's 29 electoral votes, but it wants to lock up the state to pad a margin of victory over Trump, who has for months questioned the legitimacy of an election where many people will cast mail-in ballots during the pandemic. Biden has vowed to win Pennsylvania, but if he falls short, his path to victory narrows substantially.

Trump narrowly flipped Michigan, Pennsylvania and Wisconsin in 2016, and he has virtually no path to reelection without holding at least one of them. Aides have concluded that Michigan may be out of reach amid the pandemic and that Trump faces a stubborn deficit in Wisconsin. Even if he wins there, though, he may still need to make up Electoral College ground if Biden claims Florida or the traditionally red state of Arizona.

The president’s travel this week reflects that bind. He's visiting Pennsylvania and Florida and another battleground state he likely can’t win without — North Carolina — as well as those he once thought were in his grasp — Iowa and Georgia — but where he now needs to play defense in light of recent polling showing Biden improving.

With 20 electoral votes, Pennsylvania is anchored by Philadelphia to the east, Pittsburgh to the west. But the rest of the state is largely rural, comprised of small cities and towns where Trump ran up the score four years ago. He will need to again, in even greater numbers, as his prospects have slipped since 2016 in places like vote-rich suburban Philadelphia, where he underperformed by past Republican measures.

Trump's rally is at the airport in Johnstown in Cambria County, a historically coal and steel area that narrowly backed Democrat Barack Obama in 2008. But it has trended Republican for the past three decades and, in the 2016 election, Trump scored a 37 percentage-point victory. The area is also substantially whiter and has lower median incomes and lower rates of college-degree attainment than the rest of Pennsylvania.

Given that his local support was so strong four years, it might be hard to find additional votes to make up for losses elsewhere, said former Rep. Ryan Costello, a Republican from Democratic-trending Chester County, southwest of Philadelphia.

“I don’t accept the premise that he will keep his deficit in the suburbs to what it was, or even similar, in 2016," Costello, who retired from Congress in 2019, said of Trump.

Biden visited Johnstown late last month. The former vice president has tried to cast himself as a champion of working-class voters while accusing Trump of focusing on stock market returns and Park Avenue values.

Despite the pandemic, Trump’s campaign has prioritized in-person events and aggressive door-knocking as it tries to turn out new and low propensity voters, including more members of the white working class who may have backed Democrats in the past but now favor the president.

Republicans point to an aging population and a shrinking voter-registration edge for Democrats, down 20% from 2016’s election to 717,000, according to the latest Pennsylvania data.

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Weissert reported from Washington; Lemire from New York. Associated Press writers Kevin Freking in Washington, Bill Barrow in Pembroke Pines, Fla., Thomas Beaumont in Des Moines, Iowa, and Marc Levy in Harrisburg, Pa., contributed to this report.