It is about momentum.

Trump is a candidate with no political experience, who claims to speak for the silent majority of the GOP. This allows him to be as disgusting and volatile as he wants - playing "little hitler" and all the unfounded talk about a wall, etc. These racist and cruel concepts will be treated as legitimate as long as it is honestly believed that Trump does, in fact, speak for a silent majority. That these beliefs somehow found most people's conservitism.

The Iowa caucus destroys the idea. It makes it clear that Trump only speaks for around 20% of the GOP, and that the real silent majority, what in years past was rightfully called the establishment, is just waiting in the wings to vote for Rubio.

And it's not really about percentage or votes. It's about shifting landscapes. Rubio way outporformed, he very nearly got second place. Cruz also outporformed and had a good showing. But Trump simply didn't shift at all, his support being less then expected if anything.

People are quick to push the whole winning thing. But Trump could have easily come in second and moved forward to win the nomination. But the most importent thing for Trump was that he had to prove he lived up to the hype. He had to prove his people would come out, that even if Cruz beat him in Iowa - which has always been a possibility - nobody else would threaten him in the future primaries.

But he failed to prove that. Combine a generally weak performance by him (compared to Cruz) and Rubio ' massive surge, and Trump looks a hell of a lot more valnerable, and a hell of a lot less like the Republican nominee. All we are waiting for is for Christie, Kasich, and Bush to drop out and Rubio will be the nominee, guarenteed.

I don't expect Trump to win a single primary at this point.