A look at the exit polls from Wisconsin on Tuesday night suggests that Donald Trump's problem in the state wasn't that he lost support from earlier in the year; it was that he didn't gain any. In Marquette University's poll in late February, Trump had the support of 30 percent of Republicans in the state. In their poll late last month, he had the same 30 percent. During that same period, Cruz went from 19 percent to 40 percent. In the end, Cruz did better than the Real Clear Politics average. Trump did about as expected -- 35 percent.

In 2012, the front-runner after the same number of contests (36) was Mitt Romney. He'd been beaten a number of times, but he kept accruing delegates. It was after the first 36 contests (in red below) that Romney pulled away, not getting fewer than 50 percent of the vote in any of the remaining states (in yellow).

(Territories are in light pink. They generally have more volatile results.)

Compare the Romney pattern with Trump's pattern this year.

Trump still hasn't cracked 50 percent in any contest. Notice that, with the exception of the Northern Marianas, his results are pretty flat.

We can overlay trendlines in the contests.

Trump's results have trended up slightly. Cruz's and Kasich's have trended up much more. As predicted, support consolidated against Trump.

In 2012, Romney, Rick Santorum and Newt Gingrich each did about the same in the 27th through 36th contests as they did in the 1st through 36th. In 2016, Trump has done the same in all of the contests as he has recently -- but his competitors have gained. If you take out the Marianas, in fact, Trump's done worse in recent contests than overall.

This is Trump's problem in a nutshell. By this point four years ago, Romney was starting to prep for the general election. Trump looks like he may not get there.