The super PAC has sent similar videos of Trump-endorsed candidates to voters in Arizona, Ohio, Michigan and Nevada.
For Mr. Trump and Mr. Biden, the stakes could extend well beyond this year’s fight for control of Congress.
Already, both men have taken early steps toward announcing another run for president in 2024.
Mr. Trump has relentlessly teased supporters about a third White House campaign, and is expected to formally announce another bid soon after the midterms.
Mr. Biden has suggested that he would be more likely to run if Mr. Trump enters the race, with people close to the president saying they believe he is the Democrat best positioned to defeat his former opponent. Still, Mr. Biden, who will turn 80 this month, has shown signs of political weakness, even among his base.
But whether significant midterm losses for Democrats would weaken Mr. Biden’s argument for a re-election bid remains an open question. Celinda Lake, a Democratic pollster and a longtime ally of the president, said the midterm outcome would not affect his decision.
“He is running,” she said. “Did Obama not run? Did George Bush Sr. not run? No. They all run. They all have bad first midterms, and they all run.”
At an early voting site near downtown Atlanta, the heart of Georgia’s Democratic stronghold, April Ledbetter, 43, a recording studio owner and a lifelong Democrat, said she worried that Mr. Biden’s low approval rating in the state was hurting Stacey Abrams, the Democratic nominee for governor.
“I feel like he’s probably impacting Abrams’s chance of getting elected,” Ms. Ledbetter said. “I kind of hope he doesn’t run again. I hope that somebody else steps in, because I’m not sure that he’d really be able to do it again.”
Lisa Lerer reported from Philadelphia, and Michael C. Bender from Washington. Katie Glueck contributed reporting from Philadelphia, and Maya King from Atlanta.
