2012: President Joe Biden vs. Donald Trump

[President Johnson]

Joe Biden wins the 2008 Democratic nomination and defeats John McCain in November. His presidency mainly goes as Obama's. In 2012, Donald Trump wins the Republican nomination in a crowded field and becomes President Biden's challenger. How does the election turn out?

[Chips]

Joe Biden/Barack Obama: 279 electoral votes and 51% of the popular vote
Donald Trump/Marco Rubio: 259 electoral votes and 48% of the popular vote

[NewYorkExpress]

I don't think Trump would run against an incumbent Biden in 2012, because a lot of his actions in 2012 and 2016 were motivated by racism against Obama.

If Trump does win the nomination...

Biden's stimulus policies, and lack of willingness to remove troops from Iraq hurt him. In addition his IRL opposition to killing Osama Bin Laden, means he probably wouldn't have sanctioned the SEAL Team Six mission to kill him.

President Joe Biden/Vice President Barack Obama 268 Electoral Votes 50% of the Popular Vote
Businessman Donald Trump/Senator Jim DeMint 270 Electoral Votes 49% of the Popular Vote.

[Alben Barkley]

I don't think Trump would run against an incumbent Biden in 2012, because a lot of his actions in 2012 and 2016 were motivated by racism against Obama.

If Trump does win the nomination...

Biden's stimulus policies, and lack of willingness to remove troops from Iraq hurt him. In addition his IRL opposition to killing Osama Bin Laden, means he probably wouldn't have sanctioned the SEAL Team Six mission to kill him.

President Joe Biden/Vice President Barack Obama 268 Electoral Votes 50% of the Popular Vote
Businessman Donald Trump/Senator Jim DeMint 270 Electoral Votes 49% of the Popular Vote.

Even if all that's true (big if), I don't see Trump beating Biden in 2012 under any circumstances. That was not a populist year, and it wouldn't be fueled by racial resentment and sexism in the way 2016 was. (As you say part of the reason Trump got into politics was a racist backlash to Obama.) Trump was uniquely well-suited against Hillary, and is pretty poorly-suited against Biden even this year, let alone then. No chance he flips the rust belt at that time against Biden. Especially not if Biden's holding on to Florida and Iowa. That makes no sense.

[President Biden Democrat]

This would have never happened but if it for some reason did, Biden would have definitely won. After 4 years of a Democratic candidate, the country overall was doing well and Biden would have been able to win the midwest, and other places as well. I'd probably say the margin would be 308 to 230 in favor of President Biden. Trump maybe would be able to win in Ohio and Iowa, and Biden would take the midwest and Florida, among other states as well.