Actually donated to Cruz and now think that Trump is going to take it all and Cruz’s citizenship won’t matter.
That said, one missed tactic Republican candidates could have used was somehow suggested Trump was suspending his campaign when he opted out of the debate, for example Jeb could have asked the moderators ‘he may have run out of energy, has he suspended his campaign too?’
Good humor has to have a bit of truth in it. Jeb saying Trump does not have energy is not believable. Trump has very good timing and a nose for humor, Jeb not really.