You are assuming that Trump is the only candidate that can win and you are correct with respect to the thinking of the voter base of which we are both members. And I am not so naive to believe that Romney’s current call to support Cruz would last any longer than the first convention vote. I tend to go with the notion that avid Trump supporters believe he can win but the establishment likely knows he cannot. Do I trust the establishment more than my own instincts? Not necessarily, but I certainly don’t discount their fears or their actions to deny Trump the nomination if he does not have a delegate majority going in. And if in that case, the convention results in someone other than Trump, that nominee must be actively supported to keep the Hillary disaster from even getting close to the White House.
Romney essentially said he endorsed Cruz for the sole purpose of denying Trump enough delegates to win...in order setup the ability pick someone else at the convention....someone in the same vein as the shit sandwiches the GOPe has continued to serve up the last few election cycles.
That WON’T work anymore, and is guaranteed to elect Hitlery...unless Trump rightfully tells the GOPe to go pound sand and runs third party, which at that point I would have to support.