Former Vice President Joe Biden boarded a new campaign plane in Wilmington, Delaware, at 3:18pm as he gets ready to head to Cleveland, Ohio, for the debate tonight.

-ABC News' Molly Nagle

Overwhelming support in Philadelphia and its suburbs lift former Vice President Joe Biden to a clear lead in crucial Pennsylvania, with backing from college-educated white people and women -- notably white, moderate and suburban women -- central to his advantage in a new ABC News/Washington Post poll.

President Donald Trump, for his part, is suffering attrition among his 2016 supporters; 8% of them now back Biden instead. While a small slice of the electorate, it’s a potentially important factor in a state Trump won by 44,292 votes out of nearly 6.2 million cast four years ago.

Likely voters support Biden over Trump by 54 to 45%, almost exactly matching a national ABC/Post poll released Sunday. The result includes more than a 2 to 1 Biden lead in the populous Philadelphia suburbs, home to nearly a quarter of likely voters, and close results in northeastern and western Pennsylvania, leaving only the conservative center of the state clearly to Trump.

See more data on this new poll here.

-Gary Langer of Langer Research Associates, conducted the poll.

-ABC News' Isabella Meneses contributed to this report.

The Biden campaign released Joe Biden and Kamala Harris’ 2019 tax returns, a clear effort to draw a sharp contrast with the revelations about Trump’s tax returns reported by the New York Times, ahead of tonight’s debate.

With Tuesday’s release Biden has made public 22 years of records, and Harris 15 years.

The releases were posted to Biden’s campaign site.

-ABC News' Mary Bruce and Molly Nagle

With unprecedented unemployment in the United States, where health care is inextricably linked to employment, and a coronavirus pandemic ravaging the globe, it's safe to say that on Nov. 3, health is on the ballot.

As it stands, more than 200,000 Americans have died of COVID-19. Another 13 million are unemployed.

Health might be a political football in 2020, but it's also a deeply personal issue that affects every American voter. Given health's crucial significance this year, the nonprofit Commonwealth Fund polled 4,220 likely voters in battleground states between Aug. 25 and Sept. 20 on which health care issues mattered most to them, and which candidate -- President Donald Trump or former Vice President Joe Biden -- they thought would be more likely to address those health concerns.

Here's what the American public said about which health care issues they care about, in advance of the first presidential debate.

-ABC News' Erin Schumaker

Russia's ongoing brazen efforts to interfere in the presidential election -- as they did four years ago -- remains a principal concern among national security officials, along with other adversaries including China. But unlike in 2016, the rapid and sweeping embrace of vote-by-mail in response to the coronavirus pandemic injects new uncertainty about election security, as millions prepare to vote in an alternative way.

Fueling those anxieties over mail voting, which is underway in several states, is President Trump’s unsubstantiated allegations of rampant fraud, even as dozens of state election officials tell ABC News that they have confidence in the system. His campaign against vote-by-mail throughout the cycle exceeds similar efforts he made in 2016, when he argued, without evidence, that voter fraud was the only reason Hillary Clinton won the popular vote. His own voting integrity commission found no evidence of that.

The integrity of this year's matchup between Trump and former Vice President Joe Biden has taken on an outsized role in the increasingly competitive political environment, as attempts to undermine confidence in the democratic process mount both from outside the country's borders and from inside the Oval Office.

Biden has attempted to combat Trump’s onslaught by pointing out that Trump himself has voted-by-mail in Florida from the White House.

Some elections experts argue Trump’s offensive against mail-in voting is a voter suppression tool, which could lay the "groundwork for contesting a close election if he loses, " wrote Rick Hasen, a professor of law and political science at the University of California, Irvine, and the author of "Election Meltdown: Dirty Tricks, Distrust and the Threat to American Democracy."

"The most benign explanation for Mr. Trump’s obsessive focus on mail-in balloting is that he is looking for an excuse for a possible loss to his Democratic opponent, Joe Biden, in November. The less benign explanation is that he is seeking to sow chaos to drive down turnout and undermine the legitimacy of the election," wrote Hasen,.

At the first presidential debate on Tuesday at Case Western Reserve University in Cleveland, Ohio, the two rivals are set to spar over the integrity of the election, one of the topics previewed by the Commission on Presidential Debates.

Here's what we know about the candidates' histories with and stances on the issue

-ABC News' Kendall Karson and Quinn Scanlan