Any candidate who wins at least 270 electoral college (EC) votes has the only mandate that matters - the Constitutional authority and responsibility to be the President of the United States, answerable to all Americans.
As of this writing, Joe Biden has 290 EC votes to Donald Trump's 214, with a decisive edge in the popular vote of more than 4.5 million.
If (as seems likely) Biden's edge continues to expand past the current 10,000 votes in GA, he'll have 306 EC votes to Trump's 232 (including NC and AK, which have yet to be called, in the Trump column).
In case you still have any doubts about the validity of that edge, here are 5 presidents who won 6 elections by slimmer margins in the past 60 years (including Trump 2016):
- John F Kennedy won with 303 EC votes, having won the popular vote by just over 100k
- Richard Nixon won with 301 EC votes in 1968, having won the popular vote by over half a million
- Jimmy Carter won with 297 EC votes in 1976, having won the popular vote by more than 1.5 million
- George W. Bush won with 271 EC votes in 2000, having lost the popular vote by more than half a million
- George W. Bush won with 286 EC votes in 2004, having won the popular vote by over 3 million
- Donald Trump won with 304 EC votes in 2016, having lost the popular vote by nearly 3 million
Thus, before you buy into the denial of reality and the rush to burn democracy to the ground before conceding defeat, consider that this is what democracy in action looks like.
Those who despise Trump and hate everything he says and does had to accept that he was the president when he won the EC in 2016, despite losing the popular vote by nearly 3 million.
Now the shoe is being fit to the other foot. It may not be comfortable, but that's the way our system is set up. If you don't like it, you're free to work diligently to change it to something more to your liking, if you can get enough momentum to pass a Constitutional amendment.
Just please remember that as much as you may disagree with your political opponents, we're still all Americans who love our country and want what's best for it. We can certainly hold the opinion (or even conviction) that the other side is wrong, but we hold them as enemies at the peril of our nation.