President Trump is on his way to Ohio ahead of the debate tonight and while he didn't speak to reporters before departing, his chief of staff Mark Meadows said that Trump was essentially done preparing for the debate and added that he was in a good mood.

Meadows said that some of the debate guests would be traveling on Air Force One, but didn't name names. However Alice Johnson, who Trump pardoned last month, was spotted boarding.

In addition to Johnson, the pool traveling with the president so far has spotted Lara Trump, Eric Trump, Tiffany Trump, Donald Trump Jr. and Kim Guilfoyle aboard Air Force One.

-ABC News' Katherine Faulders

Despite Republican successes in statewide races in Ohio since 2016, the Buckeye State has become increasingly competitive as Trump and former vice president Joe Biden prepare to face off in Cleveland for their first debate on Tuesday.

In recent weeks Trump and Vice President Mike Pence have traveled repeatedly to Ohio, where they defeated Hillary Clinton and Sen. Tim Kaine, D-Va., her vice presidential candidate, in 2016, 51% to 43%.

Republicans also performed well statewide two years ago, winning the gubernatorial race and other down-ballot contests.

“Ohioans showed up for President Trump in 2016 and we expect them to do the same this November,” Trump campaign spokeswoman Samantha Zager told ABC News.

The president’s campaign has had a permanent presence on the ground in Ohio since 2016, and said they have made more than 10 million voter contacts in the state, where they and other GOP groups continue to canvass on the ground during the coronavirus pandemic.

The Biden campaign, meanwhile, has relied on virtual and digital organizing in the state during the pandemic, and has hosted hundreds of events and held 450,000 conversations with voters over the last month. Following Tuesday's debate, Biden will take a train tour of the state on Wednesday.

Biden has delivered a sharp economic message focused on Trump's record, centered on Toledo and Youngstown, home to several car plants and many blue-collar voters who abandoned Democrats and voted for Trump for years ago.

He's run at least eight television ads in recent weeks, including a response to Trump's call for a ban on Goodyear, the Ohio-based tire company than ran in Akron, where the company is based.

In an election year reshaped by the coronavirus pandemic, it’s also playing host to a number of legal battles over access to ballot drop boxes, which are increasingly used by voters as an alternative to in-person voting or relying on the United States Postal Service, amid concerns about service delays.

Read more about the battle for Ohio here.

-ABC News' Ben Siegel and Adia Robinson

An immutable fact of politics in the era of President Donald Trump is that there's no separating the president from his base.

Yet an ABC News/Washington Post poll released Tuesday morning out of critical Pennsylvania -- FiveThirtyEight's most likely tipping-point state -- brings new evidence that Trump can't bank on the range of supporters he once did.

The poll shows former Vice President Joe Biden leading Trump 54-45 among likely voters, mirroring the results of the ABC/Post national poll released Sunday. Hillary Clinton backers from 2016 support Biden 98-1 in the Pennsylvania poll, while Trump's supporters from last time break 92-8 in his favor.

This does not mark a mass exodus. But it suggests a narrowing coalition, Wisconsin and Michigan -- all states won by Trump by less than a percentage point, in a region Trump and Biden are set to visit in the days after Tuesday night's first presidential debate.

There won't be many, or perhaps any, singular moments as critical as this first debate in terms of changing the trajectory of the race. Trump wants and needs to effectively disqualify Biden as an alternative -- to make the campaign about Biden more than himself.

Biden will be trying to avoid a brawl of an insult-fest. He will be seeking to keep the campaign focused on COVID-19 and the economy -- about Trump and his leadership, in a campaign that's been more steady than not.

-ABC News Political Director Rick Klein

ABC News Chief Global Affairs correspondent Martha Raddatz joins ABC News' Start Here podcast to talk about her experience moderating debates with both President Donald Trump and former Vice President Joe Biden before the two go head-to-head for the first time Tuesday night.

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