The winner of the GOP debate? Trump

Thursday's debate was largely about the man not on the stage — Donald Trump.

Republican presidential candidate Donald Trump speaks at a veteran's rally in Des Moines, Iowa January 28, 2016.
Rick Wilking | Reuters
Republican presidential candidate Donald Trump speaks at a veteran's rally in Des Moines, Iowa January 28, 2016.

Marco Rubio and Jeb Bush both had great nights, but Bush got the better of their exchange on immigration. Bush picked the right time to shine in a debate. Ted Cruz also occupied much of the oxygen in the room, and seemed to take incoming from all sides. He handled it fine and I think probably cemented himself in second place — at least for the moment. Governors Chris Christie and John Kasich had good moments, too. In fact, on the main stage, absent Donald Trump, everyone did pretty well.

But, Trump will be the main beneficiary of the night. For starters, as the front-runner, he had little to gain from showing up. The debate moderators asked some very tough questions, and, when challenged in previous debates, Mr. Trump hasn't fared well. Trump didn't make any errors last night for the simple reason that he didn't answer any questions!

Second, Trump dominated news coverage all day leading to the debate. The first 10 minutes of the debate were largely about him and at many points in the evening; he was the elephant in the room. While Cruz was taking incoming, Trump was across town standing in front of dozens of television cameras and hundreds of adoring fans. Even though his record of donating to veterans' organizations is weak, he claims to have raised over six million dollars for a worthy cause.

Third, in taking on Fox News, Trump somehow managed to make Fox News part of the establishment, while he was an aggrieved party. He effectively presented the case that he was wronged. It was just another example of elites trying to pull one over on the "little guy." Ironic and ridiculous, yes, but it was effective nonetheless.

All in all, at the top of the race, I doubt this debate, the last before the Iowa caucuses, changes much. As for the caucuses, Trump will continue to lead the field and Cruz will remain hot on his heels. What's more interesting is how the second tier of candidates fares after last night. The little reported fact is there's a fierce race going on for second place in New Hampshire right now.

The latest poll shows two points separates Cruz, Kasich, Rubio and Bush. Christie was a bit lower, but not much. If one of these four establishment candidates finishes second to Trump in New Hampshire, watch for him to take off and finally really challenge the Donald.

Commentary by Sara Taylor Fagen, a partner at DDC Advocacy and a former Political Director for President George W. Bush. She is also a CNBC contributor. Follow her on Twitter @sarafagen2.

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