No other GOP candidate can deliver that mandate. I'm not sure very much will change overall if we get elected the typical Republican (i.e. Rubio) in a squeaker. Most likely however, a Rubio will lose just like Mitt Romney before him. And as much as we love Ted Cruz here (and I like him too), he only appeals to the conservative base - which we all know will not be enough to carry a general election. Perhaps a Trump Administration will soften the path for a Ted Cruz later on. Cruz is only 44, he'll have other chances.
As much as I like Ted Cruz - and cringe at a Trump presidency I tend to agree that Trump is our only chance to out glitz a ticket of Biden/Warren. Trump/Cruz could do it. I could see myself voting for trump ONLY if he brings Cruz as vp. Cruz would do a good job of mentoring Trump on conservatism and Christian values.
We all here have to realize the goal in any election is to defeat the opposition. We have to play to win, even if that means giving up on some things. I would cringe voting for Trump, and I would pray he listens to Cruz.
I think just about anybody could beat Hillary if she is the Rat nominee (which I doubt will happen) she is a horrible candidate. But you are right we need to win big to have a mandate. Trump has the best chance of a big win.