President Barack Obama (D-IL) / Vice President Joe Biden (D-DE) ✓
Fmr. Governor Mitt Romney (R-MA) / Congressman Paul Ryan (R-WI)
Businessman Donald Trump (I-NY) / Senator Jim DeMint (I-SC)
Trump's biggest effect here would be hurting Romney by making him sound weak to conservatives on every issue. Some would suspect he was a Democratic plant, but they wouldn't really be able to deny the softening effect he had on Romney's rhetoric. That said, his campaign wouldn't really gain traction as a viable alternative in the media environment of 2012. I've posted at length about the cultural factors behind Trump's popularity, all of which occurred in Obama's second term.
A Trump candidacy wouldn't be a Tea Party revolt so much as a civil war within the Tea Party (note that it wasn't a 1:1, there's plenty of overlap between the Tea Party and MAGA in its "Main Street USA" base but plenty defected too; I know a Tea Partier who was in it for the small-government angle that became a Never Trumper), plus some of what were the Obama-Trump voters IOTL. I think the religious right would reject Trump's uncouthness given a more palatable-ish option in Romney as they hadn't gotten quite so desperate yet. The younger online alt-right aspect of his movement IOTL wouldn't be a thing pre-Gamergate, although the much smaller Paulbot cohort would be a token part of his coalition here. Not a total wipeout for Romney but hurts bad. I'm iffy on South Carolina but DeMint pushes it over the line here.
