Some (or, a lot of) coaching, ability to emphasize his military record in a mostly national security-based election against Wolf, embracing of immigration reform, and deciding not to contest social issues other than abortion (gay marriage being legal at this point in all 50 states and therefore a dead issue--the GOP platform that year omitted any mention of it), and endorsement of a minimum wage raise to $11 (which was actually passed in 2021), which is based on his OTL endorsement of the Arkansas minimum wage ballot initiative.
I hate to say this, but none of this is at all likely, and even if he did *do* any of that, he'd be risking alienating enough of his particular base to swing the election to the Democrat(Tom Wolf, in this case), whom quite a few independents would still vote for anyway, even if mainly out of disgust for what many of them would see as flip-flopping or even hypocrisy on the part of the GOP(it's a good part of the reason Romney lost in 2012, and he's possibly the least extremist candidate the GOP had offered then!).
Hey, man, I don't want to be too hard on you here: I do like what you've done with Russia, and this whole TL in general has potential. But if you really want a realistic scenario in regards to America, I'd suggest having Tom Wolf win in 2020, or, if you feel you absolutely must have a Republican, I would go with Susan Collins or Rob Portman; Collins, especially, doesn't have the stigmas that are already and would continue to be associated with any other GOP candidate, and, because of that, would actually have a solid chance of winning over enough independents to win the White House, and the same goes for Portman(or Lisa Murkowski, even!) as well, even if quite a bit of the Teabagger base gets alienated in the process.