Joe Biden has promised supporters "we're going to win this", as the race for the White House remains on a knife edge.
Addressing Americans at a drive-in rally he likely hoped would have been the site of a victory speech in Delaware, the Democrat challenger said people should "keep the faith" while vote counting continues.
"It may take a little longer," he warned, after crucial swing states he hoped to flip like Arizona, Georgia, North Carolina and Wisconsin went down to the wire, remaining too close to call.
And others he wanted to turn blue - Michigan and Pennsylvania - face severe reporting delays, with no official result likely this morning.
It means an intense showdown continues between the two candidates, with Mr Trump fighting to avoid becoming the first one-term president in decades.
"We're gonna have to be patient, until the hard work of tallying votes is finished," Mr Biden said, in a speech that lasted only a few minutes, adding: "It ain't over 'til every ballot is counted."
A bullish Donald Trump tweeted in response from the White House where he is watching the results unfold: "We are up BIG, but they are trying to STEAL the Election.
"We will never let them do it. Votes cannot be cast after the Poles [sic] are closed!"
He appeared to be referring to a decision by the Supreme Court to allow mail-in ballots in Pennsylvania to be counted up to three days after the election.
Twitter stepped in again to censor Mr Trump's post, labelling it with the warning: "Some or all of the content shared in this tweet is disputed and might be misleading about an election or other civic process."
In a boost for Mr Biden, he is leading by around 150,000 votes in the race for Arizona - a significant flip if he can pull it off, since the last Democrat win there was in 1996.
His campaign told NBC the competition nationally remains a "slog", as the margin between him and Mr Trump is very close.
They are still "confident" of winning enough crucial battleground states to hit the 270 Electoral College (EC) votes needed to clinch the presidency.
While the results have not yet been officially announced, Sky News/ NBC projections show Mr Trump is on course to hold on to Ohio, Florida, Iowa and Texas.
They will come as a serious blow to Mr Biden, who set his sights high on "ruby red" targets but has failed to pull off the convincing, early win he will have hoped for.
But the Democrats are projected to retain control of the House of Representatives.
