NEW YORK CITY - SEPTEMBER 3 2015: Republican candidate for president Donald Trump announced he had signed a pledge not to run as an independent candidate should he fail to win the party's nomination in 2016.

Tonight is all about Ted Cruz vs. Marco Rubio, Not Trump v. Cruz

It’s obvious. The media and the pundits have been waiting for Donald Trump and Ted Cruz to blow each other up and leave neither man standing. They positively relish the idea of this fight. And it is an obvious one. Wolf Blitzer, at the CNN debate, will no doubt set up questions to draw out that fight.

But don’t look there. That’s not the real fight.

The real fight on stage tonight is going to be Ted Cruz vs. Marco Rubio. Rubio needs to hold on to the establishment as Bush fades. Cruz needs to convince the establishment that he is the only guy who can take on Trump. Rubio needs conservatives to give him a second chance after his Gang of Eight deal. Cruz needs to hold conservatives and convince them his mastery of debate and willingness to fight overcomes Rubio’s communication skills.

In the last debate, Cruz took a subtle dig at Rubio on sugar subsidies. Since then, Rubio’s Super PAC has gone after Cruz on national security. Rubio has suggested Cruz would be weaker on national security.

Cruz has gone after Rubio as a neocon internationalist who agreed with Barack Obama on Libya and Syria.

That’s where the fight is going to be tonight. Cruz v. Trump will be gravy. Cruz v. Rubio will be the real fight.