Part of Romney's attraction is his business knowledge and experience. Trump undercuts that support base. His potty-mouth straight talk gives real legitimacy to the outsider claim, rather than Romney's halfhearted one as a former governor of Massachusetts. And Trump undercuts the non-Evangelical support that Romney's getting. Could Palin claim a lot of these voters? Sure. Can she get them in the first few primaries, especially the open primaries? Don't think so, unless someone splits off Romney's votes and evens out the field.
I think it's a three horse race with Trump in it, or a one horse with Romney.
I don’t see any of Romney’s votes being outsider-driven, and I think Trump takes more outsider votes from Palin than Romney. But I actually think he’s both shot his wad in terms of primary viability and has enough reason to stay out of the primaries anyway.
But we can just disagree on his influence for the race.