Cruz is simply a stalking horse prancing about to make Trump look bad. He has no chance of actually becoming the GOP nominee, but he's being a loyal party soldier by playing the part assigned to him to draw fire in order to highlight Donald's alleged deficiencies ie emotionally unstable.
Now, of course the Trump team knows this perfectly well. Their challenge is to both respond in forceful manner to uphold his reputation for never backing down. But, he also has to pivot effectively to counter the obvious GOP meme being set up.
That's the real beauty of watching this play out. Better than a grand master chess tournament.
I think he's about to go nuclear.
Ted Cruz must be wondering what's going on.