Maine and Nebraska are the only two states that allow a split electoral vote, with Nebraska having 5 electoral votes and Maine having 4 electoral votes.
But in 2008, Barack Obama won one electoral vote in Nebraska, while the state majority went Republican.
And in 2016, Donald Trump won one electoral vote in Maine, while the state majority went Democratic.
Assuming Joe Biden won back just two Trump states from 2016–Pennsylvania and Michigan, but failed to win back Wisconsin, Ohio, Iowa, and Florida, other Obama states in 2012 lost by Hillary Clinton in 2016, the following possible scenarios could occur!
We would go from 306 for Trump and subtract 20 for Pennsylvania and 16 for Michigan, and Biden would win with exactly 270 electoral votes!
But if the one Maine district stayed with Trump, the electoral vote would be a tie, 269-269, and the House of Representatives would choose the President, as they did in 1800 and 1824, with each state having one vote based on the majority of either party holding Congressional seats in each state.
But the 269-269 vote could be overcome if the one Nebraska district switched to support of Biden, as it did for Obama in 2008, and Biden would have 270 electoral votes!
Right now 26 states have Republican majority delegations, but that could change, if the Democrats were able to win two more states with a majority delegation of their party.
Of course, seven states only have one House member, so that person alone determines the state vote in those seven states.
Also, if we ended up with 25 states having a Republican and 25 having Democratic majority delegations, then there would be a massive constitutional crisis with the tie that would exist!
We could have Inauguration Day approach, and no certainty that either Joe Biden or Donald Trump would be declared the winner.
So then, Nancy Pelosi, assuming the House of Representatives stayed in Democratic hands, would become Acting President until, somehow, the deadlock was broken!