WASHINGTON - Under America's political system, a presidential election is won not by the candidate who gets the highest number of votes from Americans overall, but by the one who gets at least 270 of the 538 electoral votes allotted to all 50 states and Washington, DC.
The contest will be decided by a handful of battleground states that could swing either way. Here's a look at the states that matter and how they are faring.
Florida - Trump wins
Number of electoral votes: 29
Mr Donald Trump defeated Mr Joe Biden in Florida, the Associated Press projected, securing a key swing state in his bid for re-election. He had earlier held a narrow lead in the state after outperforming in one of its most populous counties, Miami-Dade.
Florida is a very diverse and competitive state that propelled Mr Trump to victory in 2016 and decided the election for Mr George W. Bush in 2000.
If Mr Trump had lost Florida, he would have had a less than a 1 per cent chance of recovering to win the overall election, according to a forecast by polling site FiveThirtyEight.
Pennsylvania
Number of electoral votes: 20
RealClearPolitics polling average as at Nov 4: Biden +1.2
In Pennsylvania, the vote is expected to take days to be tabulated.
Pennsylvania state and Philadelphia city officials offered no firm estimate on Tuesday night of how much longer it will take to finish the mail-in and absentee ballots needed to determine the presidential winner in the battleground state.
Michigan - Biden wins
Michigan, with 16 electoral votes, has been won by Mr Biden, the Associated Press projected on Wednesday (Nov 4).
The Midwestern state unexpectedly went to Mr Trump by less than half a percentage point in 2016 in one of the stunning state defeats suffered by Hillary Clinton.
With Michigan's 16 electoral votes, Mr Biden now has a total of 264 electoral college votes- six shy of the magic number of 270 needed to win the US presidency, according to US network projections.
Wisconsin - Biden wins
Mr Biden has won the vital battleground of Wisconsin, flipping a state won by Mr Trump in 2016.
However, the Trump's campaign said it would demand a recount in Wisconsin, where the candidates were less than 1 percentage point apart.
Georgia - Trump's slightly ahead
Number of electoral votes: 16
RealClearPolitics polling average as at Nov 4: Trump +1
That Georgia, a long-time red state that Mr Trump won by a decent margin of 5.1 percentage points, is now a toss-up state is a sign both of how much Mr Trump has slipped and how blue the state has turned.
Mr Biden likely does not need Georgia to win but it would be a surprise if he did, a possible portent of a good night for him.
Iowa - Trump wins
Number of electoral votes: 6
Trump has won Iowa, AP reported.
Iowa swung sharply back to red in 2016, backing Mr Trump by a comfortable margin, but is now a toss-up state. Iowa is also not a must-win for Mr Biden, but if Mr Trump had lost the state, it would have been a signal that the Republican Party is weakening in the Midwest.
North Carolina - Trump's inching ahead
Number of electoral votes: 15
RealClearPolitics polling average as at Nov 4: Trump +0.2
Mr Trump was inching ahead after an earlier Biden lead in North Carolina, though there are many votes outstanding in the state.
North Carolina has voted Republican all but two times since the 1970s. North Carolina, together with Florida, Georgia and Ohio, are toss-up states Mr Trump all but needs to win re-election.
If Mr Biden wins North Carolina, that might indicate that he will go on to win other states that Mr Trump needs as well.
Ohio - Trump wins
Number of electoral votes: 18
Mr Trump has defeated Mr Biden in Ohio, AP reported.
No Republican candidate has ever won the White House without winning Ohio, the state with the track record of voting for every winner since 1944 with a single exception. If Mr Trump had lost Ohio, it would have been likely that things are going badly in the Midwest for him.
Texas - Trump wins
Number of electoral votes: 38
Texas, with its 38 electoral votes, is a big prize for Mr Trump.
It is traditionally a staunchly Republican state but Mr Biden made major inroads in the campaign and it was thought the state could go blue for the first time since 1976.
Arizona - Biden wins
Number of electoral votes: 11
Mr Biden became the first Democratic presidential candidate to win Arizona since 1996.
He benefited from a more diverse electorate in Arizona, which Mr Trump won by 3.5 percentage points in 2016. Mr Bill Clinton was the last Democrat to win Arizona, claiming it for his re-election.
Arizona has long voted Republican but has shown signs of shifting somewhat blue in recent years, as the proportion of Latino voters in the state has grown.
In 2018, a Democrat - Ms Krysten Sinema - won a Senate seat for the first time in the state since 1988.
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