Trump, down in the polls to Biden and facing a once-unimaginable cash crunch, has been forced to spend the dwindling final weeks of his reelection fight on defense.

Out of the 13 rallies in nine states that the president has scheduled since returning to the campaign trail after being diagnosed with COVID-19, only one, Nevada, would be a pickup for the president -- the others show a president needing to spend valuable time and money predominantly campaigning in states he won in 2016, including some he won handily like Iowa.

Publicly, the Trump campaign remains optimistic.

Internally, the Trump campaign is increasingly worried that the president's chances of winning North Carolina, a state the team has heavily invested in and views as essential for Trump's path to victory, has all but evaporated. The campaign had viewed the state as "super safe" as recently as just a few weeks ago, sources told ABC News.

Advisers now fear that, because the state counts and reports both day-of and mail-in votes together on election night, losing North Carolina could be a clear white flag.

And with the fallout from the first debate and Trump's contracting the novel coronavirus, some aides inside the campaign have started to grow fearful of what their employment prospects may look like if the president were to lose, sources said.

-ABC News’ Will Steakin and Soo Rin Kim

Early voting has begun in Florida, a state key to a Trump or Biden victory.

Of the state's 67 counties, 52 are opening their polling sites to an electorate eager to determine the outcome of one of the nation's most critical battlegrounds.

Democratic vice-presidential candidate Sen. Kamala Harris is slated to attend a drive-in rally in Orlando mid-morning and a voter mobilization event in Jacksonville in late afternoon.

As of Sunday, a staggering 2.5 million Floridians had already cast their ballots by mail -- only 200,000 shy of 2016's entire vote-by-mail total. Most polls in the state still show a tight contest between Trump and Biden.

With every state having some form of voting now underway, an unprecedented 28,117,692 voters have already voted and at least 82,013,225 ballots have been requested in early voting states, according to the United States Elections Project, spearheaded by University of Florida's political expert Michael McDonald.

If Trump's worst enemy has always been himself, Biden's most important opponent at the moment might be his own party -- its memories, its anxieties and its growing expectations.

Fifteen days out from Election Day, any honest reading of the data suggests that this is Biden's race to lose. The race's stubborn fundamentals are combining with COVID-19 spikes and the president's scattered messaging, while 28 million Americans and counting have already cast ballots.

Democrats, of course, are terrified that Biden could still lose. The buzz in numbers-obsessed circles is about party registration gaps and early vote spikes among white, non-college voters; the word from the Biden campaign is not to put stock in public polling and to expect a nasty finish.

It's easy to see Trump's late-stage attacks on Biden and his family, along with his squabbles with fellow Republicans, and view it as self-destructive or simply irrelevant. Add Sen. John Cornyn, R-Texas, to a growing list of incumbents in tight races to put distance between himself and Trump, and welcome Sen. Ben Sasse, R-Neb., back to Trump's Twitter attack list.

But even those story lines carry a gnawing familiarity to Democrats who remember how messy the last few weeks of the last campaign really were. Running confident is less appealing than running scared, at least for now.

-ABC News Political Director Rick Klein