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Former Vice President Joe Biden criticized President Trump's mask-wearing habits on Sunday, telling a Pennsylvania rally that the impact of the COVID-19 pandemic wouldn't have been as great if Trump had been better about wearing one.

"Imagine where we'd be if this president just wore a mask instead of mocked it from the beginning -- I can tell you this. And every major health expert agrees with me," he said.

"And I can tell you this, we wouldn't have 9 million confirmed cases of COVID in this nation. We wouldn't have over 230,000 dead -- almost 9,000 here in Pennsylvania. We wouldn't be seeing those new record numbers of cases we're seeing every day now."

Biden's comments came as the pandemic dominated media coverage before the election on Tuesday. He didn't present  evidence for this claim, but his criticism reflected that of others who argued that the president set a poor example with his mask-wearing habits and his derisive comments about Biden's mask-wearing.

BIDEN SAYS TRUMP'S CORONAVIRUS RESPONSE 'ALMOST CRIMINAL' DURING RALLY IN PHILADELPHIA

President Trump has long faced criticism for not wearing a mask during the first four months of the pandemic, although members of his administration have, for months, advised the public to wear face coverings.

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In July, Trump tweeted a photo of himself wearing a mask, saying the country was "united" to defeat COVID-19.

As of Sunday night, 230,934 American lives have been lost to the virus, with more than 9.1 million cases in the country. Infectious diseases expert Dr. Anthony Fauci told the Washington Post that with cases surging across the country, the U.S. is "in for a whole lot of hurt" in the coming months of fall and winter. 

Pointing to a previous prediction that more than 2 million people would die, Trump has claimed the pandemic could've been a lot worse without his leadership. However, that prediction was based on a study analyzing what would happen if governments and individuals in the U.S. and U.K. did absolutely nothing to change their behaviors -- meaning no distancing and no masks at all.

“I don’t think we can say we’ve prevented 2 million deaths, because people are still dying,” said Justin Lessler, an associate professor of epidemiology at Johns Hopkins Bloomberg School of Public Health, in a Kaiser Health News story fact-checking Trump's claims.

Although the president has credited his China travel ban with saving lives by preventing new cases from reaching the U.S., experts have cautioned that the bans impacting China and Europe were put in place after cases had already reached America. Separate investigations by The Associated Press and The New York Times found that thousands of travelers still arrived to the U.S. after the bans were put in place.