If Trump thinks he can win, I believe he’ll run again. If Romney challenges Trump I wouldn’t be in the least surprised to see many Republican officials and voters shift to his camp and possibly take the nomination away from Trump. Understanding history’s lessons, things are much different today and Trump is the most different person ever to become president. After 4 years of Trump it’s entirely possible that the Republican Party could choose to get behind Romney, seeing it as the party’s only chance to hold onto the White House.
But who knows? Two years is an eternity from now.
Indeed, two years is an eternity. Perhaps history does tell us something, most of the Republican leaders, establishment if you will for lack of a better word. They were against Trump from the beginning. But Trump had a hard core constituency, faction within the GOP of approximately 35%. Far from a majority, but in an 18 candidate field, more than enough to sweep up delegates with 30-35% winning the primaries. Even when the candidates narrowed, those leaders, the establishment, lifelong republicans, weren't able to decide on a single candidate to challenge Trump. In a huge field, it pays to have the largest faction of loyal supporters.
Yes, Trump is unique in his behavior, very unpresidential, uncouth from my point of view. He has lost the independent voters as of now that propelled him into the white house. I can see those same party leaders backing Romney if Trump does run again, but I think it would be to the same no avail with the largest faction within the GOP. That faction has grown, call them avid Trumpers from 35% to around 60% of the party. I think most party leaders do not fall into the avid Trumper category or even a lot of their elected officials. To go against Trump risks the wrath of those avid Trumper's who make up a slight majority of the party today.
Regardless whether it is Trump, Romney or someone else, I highly doubt due to the independent voter dislike of Trump that they can be won back in time for the 2020 general election. That is unless the democrats nominate another Hillary Clinton type candidate. then all bets are off.