Consider this an addendum of sorts.
Having made my case in the best way possible for the idea that Rubio has the better (really, only) chance to beat Trump in the GOP nomination, it is time for a caveat. The one thing Rubio has not demonstrated an ability to do, which he absolutely must do tonight (and no later), is to take on Trump head on. He absolutely must demonstrate that he can do it or he risks losing the momentum that he is gathering right now.
I know that I am not the only one who is tired of the constant back and forth between Rubio and Cruz in this fight. If I have to hear one more time the same argument over whether Ted Cruz meant for the Gang of 8 bill to pass, or whether Rubio meant for his own bill to pass, or who said what about a path to legalization, I might scream. Literally everyone knows by this point what was said and done during that time period and the voters are perfectly capable of making up their mind on this issue.
The political strategery of both Cruz and Rubio to this point has been wrong. They have both assumed that if they were the last Republican standing against Trump, they would win. They have thus combined to do a truly astounding job of ignoring the front runner on the erroneous assumption that he would crumble underneath his own weight until it has become at least probably too late. An astonishingly small percentage of television ads that have been run this election season have been run against Trump. Both Cruz and Rubio have had more negative ads unleashed against them (primarily by each other although Jeb Bush and his Super PACs have certainly helped) than literally anyone has leveled against Trump.
The end result of this strategy is that Trump's status has elevated dangerously close to an unassailable position. Rubio has to recognize that even if all the other candidates, including Cruz, vanished from existence today, he would still have trouble on his hands in taking on Donald Trump. The failure of all the candidates - including Rubio - to confront the Trump menace and treat him like the frontrunner he was has led us into this situation, and Rubio must do his part to help undo this situation and stop attacking Cruz for political selfish reasons.
Moreover, he must prove to his remaining skeptics (and there are many) that the meltdown against Christie was truly a fluke. The reason that particular debacle was so damaging to Rubio is that it caused people to wonder how Rubio would fare in a series of debates against the even more obnoxious and bullying figure of Trump. He can and absolutely must erase that failure tonight, on the biggest stage of his life, or this race is done for and I might as well take back everything I said this morning.
I am quite sure that Cruz is going to come after Rubio tonight with a vengeance. I would do the same if I were in Cruz's position. Rubio should respond just enough to not roll over and keep his focus on Trump.
In order to become the champ, you have to beat the champ. And it's time for Rubio to demonstrate that he can do that tonight, once and for all.