MILWAUKEE — The Wisconsin Republican primary is so critical to Donald Trump that, after having pledged "I'll be here all week" to his supporters, Trump promptly departed to Washington and other destinations for a couple of days off the trail prior to next Tuesday's vote.

The Wisconsin GOP contest is so critical to Sen. Ted Cruz that he took off to California for some fundraising and a guest spot on Jimmy Kimmel, in addition to a stop in North Dakota for its delegate convention, before returning to Wisconsin for a few more days of campaigning.

The Wisconsin primary is so critical to Gov. John Kasich that he headed to New York, where his highest-profile accomplishment was to be photographed eating pizza with a fork.

Wisconsin, home of Republican National Committee Chairman Reince Priebus and House Speaker Paul Ryan, has a prime spot on the GOP primary calendar. The April 5 election is the only event on that day, coming two weeks after the Arizona and Utah contests and two weeks before New York. So for the moment, all political eyes are on the Badger State.

In addition, the Wisconsin primary comes at a critical time for the beleaguered #NeverTrump movement. After failing to stop Trump in earlier races, the forces arrayed against Trump here in Wisconsin — that would be most of the Republican power structure, plus the state's formidable conservative talk radio hosts — see Wisconsin as the best hope to change the dynamic of the GOP race.

"I think this might be a pivot point in the election, because there is a gap right afterward," radio host and #NeverTrump star Charlie Sykes told me Thursday. "You have a time for the opposition to continue to re-gear. The anti-Trump political action committees are here in a very big way ... If Trump goes down in Wisconsin, those folks are going to be able to go back to their donors, their money people, and say look, this worked — all those people who said he was bulletproof were wrong."

Cruz has reason to feel confident here. After Arizona and Utah, when the campaign turned north, there were no good polls on where Wisconsin voters might be. But on Wednesday the respected Marquette Law School poll came out, showing Cruz with a 10-point lead over Trump, 40 percent to 30 percent. Later, a Fox Business poll had Cruz ahead by the same margin, 42 percent to 32 percent.

In addition, a poll by PPP, the Democratic firm, while finding a much tighter race — Cruz 38 percent to Trump 37 percent — suggested that there are "indications within the numbers that Cruz could win a wider victory."

Wisconsin will award 42 delegates — fewer than Arizona's 58 and a little more than Utah's 40. The delegates will be awarded winner-take-all in each of the state's eight congressional districts, with three delegates per district. The remaining 18 will be awarded, with a few complications, to the statewide winner.

If he prevails, Cruz could come away with a big delegate haul. Trump seems to be strong mostly in the 7th and 8th Districts, in Wisconsin's north. If those are the only two districts Trump wins, he would walk away with just six delegates, to Cruz's 36. Or perhaps Trump only wins the seventh, giving Cruz 39 delegates. Or maybe Kasich will take the 2nd District, which includes deep-blue Madison. Any of those scenarios would be a big victory for Cruz.

So what explains the candidates' movements out of Wisconsin? They are a reflection of a fundamental shift in the race in the last several days.

"The tectonic plates are moving beneath our feet," said one state GOP operative in a discussion Friday morning. "Over the course of the past week, there has been a shift of gravity where there is a sense that Cruz is going to win Wisconsin."

The operative pointed to a few key developments. First, there was not only Gov. Scott Walker's strong endorsement of Cruz, but also the endorsement of Assembly Speaker Robin Vos, who had earlier supported Marco Rubio. "Then there were rumblings in the center-right and the business community, saying 'We've got to go with Cruz,'" said the operative. "What you have seen is Walker and Speaker Vos and others sort of accepting Cruz."

That's a journey Sykes has made as well. While praising Cruz as "a principled conservative" and "a rock-solid constitutionalist," Sykes made clear that the senator from Texas wasn't anywhere near his first choice.

"I never endorsed anybody, but obviously I would have been very friendly to Walker as the favorite son," Sykes told me. "I anticipated after that that I was probably going to be supporting Rubio ... Rubio would be a natural fit; it would have been the most comfortable. I did not see myself ever supporting Cruz, quite frankly .... [But] as the field whittled down, it sort of dictated the choice."

Add to that the Marquette poll, which has been quite accurate in some Wisconsin races. (In the 2012 GOP primary, the final Marquette survey showed Mitt Romney winning by 8 points; he won by 7 points.) The Marquette results both confirmed what people were feeling about a shift in momentum to Cruz and likely contributed to an acceleration of that momentum.

Finally, Trump had a really bad week, suffering one self-inflicted wound after another. Put that all together, and the race became Cruz's to lose.

There's some question about whether that has really always been the case. While some observers saw Wisconsin as an opportunity for Trump — after all, he won next-door Michigan — others have suggested that Wisconsin, with a strong, educated, suburban Republican presence in the southeastern part of the state, lined up better for Cruz. "There's nothing about Cruz's strength and Trump weakness in Wisconsin that suggests a change in the race," the New York Times number cruncher Nate Cohn tweeted Thursday after the polls came out. "Wisconsin is Trump's second worst remaining state in our demographic model."

Now, all the candidates are returning to Wisconsin for the last days of campaigning. The picture seemed blurry when they left, but they are coming back to a race in which Cruz seems firmly in charge.