Perhaps the clearest sign that Ted Cruz is seriously challenging Donald Trump's dominance in the Republican primary race is that Trump has started attacking him.

Up until recently, the two have been operating in a state of detente, if not outright kinship. Through all the controversial statements Trump has made in this campaign, including his call last week to ban Muslims from entering the U.S., Cruz has steadfastly avoided saying anything critical of Trump, instead criticizing reporters for asking him to pass judgment on Trump's positions.

In an interview with NPR last week, Cruz was asked about the proposed Muslim ban and simply said, "I disagree with Donald on that."

But behind closed doors, Cruz was recorded saying last week that voters are asking themselves, "Who am I comfortable having their finger on the button?" In audio obtained by the New York Times, he added that, "It's also a question of judgment" — "a challenging question" for Trump, Cruz said. (He also lumped in retired neurosurgeon Ben Carson, who has sunk in polls after making serious missteps in statements about foreign policy.)

After that audio was released, Trump called out Cruz on Twitter.

A short time later, Cruz denied in a tweet that he had any issue with Trump.

But the dam appears to have broken. Since then, Trump has called Cruz a "maniac," and at an event in South Carolina over the weekend he tried to undermine Cruz's base of support among evangelical Christian conservatives based on the fact that Cruz is the son of a Cuban immigrant.

"I do like Ted Cruz, but not a lot of evangelicals come out of Cuba, in all fairness," Trump said. (In reality, a poll conducted this year showed that 5 percent of Cuban residents are evangelical.)

That was a targeted attack, since Trump has plenty of reason to worry about Cruz's position in Iowa, with its large base of evangelical voters. A Des Moines Register-Bloomberg poll released Sunday, conducted by venerable Iowa pollster J. Ann Selzer, showed Cruz opening up a 10-point lead over Trump in that state, with 45 percent of evangelicals backing Cruz.

Cruz also received the most coveted endorsement from an evangelical leader in the state last week.

There was good news for Cruz nationally over the weekend, as the latest NBC News-Wall Street Journal poll showed him jumping into second place behind Trump, 27 percent to 22 percent.

But does Cruz have a path to the nomination? The short answer is: Yes.

For casual observers of politics, Cruz might fit the mold of past candidates like Rick Santorum and Mike Huckabee — hard-core conservatives, popular with the religious base of the GOP, who won Iowa but just couldn't pull together enough support to overcome establishment candidates like John McCain and Mitt Romney.

But Cruz has some key fundamentals on his side. For one thing, he dominates the evangelical wing of the GOP, and has strong support among Tea Party backers. He's been able to raise money and build a campaign organization more effectively than Huckabee or Santorum.

The latest fundraising reports released in October showed Cruz with more cash in the bank than any other GOP candidate, with $13.8 million. Neither Santorum in the 2012 cycle nor Huckabee in the 2008 cycle reported more than $2 million cash on hand at any point in the campaign.

In states like Iowa and South Carolina, Cruz has held a massive event with thousands of supporters in attendance called the "Rally for Religious Liberty." It's a potent theme this year since the U.S. Supreme Court legalized same-sex marriage. It's also something Cruz has played up in his day job, leading the charge on Capitol Hill to pull federal funding for Planned Parenthood.

Part of the explanation of why Cruz is so well-poised is also the anti-establishment moment we are in. Cruz is very unpopular among his colleagues in Washington. In a typical election, that could make it hard to raise money and solidify a campaign. But in a GOP primary race where Washington is as good an enemy as Hillary Clinton herself, Cruz is making the most of it.

One of the consistent jokes in his stump speech goes like this: "I spent most of last week in Washington, D.C., so it is great to be back in America."

Another thing Cruz has going for him is the primary calendar, where you can see his path shaping up.

First up is Iowa on Feb. 1, where he's now leading the pack. If he wins there, he goes into New Hampshire with low stakes. No one expects Cruz to do well in New Hampshire on Feb. 9 — so he can't lose the expectations game there.

Then there's South Carolina on Feb. 20, where the vote is split among evangelical, military and establishment Republicans. Trump is leading there now, but if Cruz comes out of Iowa with a win (and the wind at his back), he could have a real shot in South Carolina, where he held one of those large rallies last month and is locking up the endorsements of pastors. Both will help in turning out evangelical voters in the state.

If Cruz were to win — or even come in a strong second — in Iowa and South Carolina, he would go into Super Tuesday on March 1 with the big mo'(mentum).

It's dominated by Southern states this year, which in the past have been marginalized in the primary calendar even though they have become the deep red heart of the Republican Party. This year, many Southern states banded together to set their primaries on this single day and create a regional superprimary, forcing candidates to spend more time campaigning in the South.

Regardless of how the politics of 2016 were shaping up, that arrangement was likely to give a strong conservative like Ted Cruz an important early boost — and a whole bunch of delegates. That day includes the GOP primary in Texas, Cruz's home state. Texas' 155 delegates are more than 10 percent of the total that a candidate needs to win the Republican nomination, though they will be awarded proportionally as opposed to winner-take-all.

This is all to say Ted Cruz has a path to the nomination that runs through Iowa and South Carolina and could carry through the Southern primaries on Super Tuesday.

Of course, others could easily spoil that. The candidate many in the Republican establishment and Beltway pundits are awaiting to challenge Trump is Florida Sen. Marco Rubio. His campaign is trying to make a big play this week as he barnstorms early voting states, including Nevada, where the GOP candidates will meet for their next debate Tuesday.

Nevada, where Rubio lived for a time as a child and maintains ties with the large Mormon community, is the only early voting state where he looks poised to succeed at this point. Of course, there's his home state of Florida as well — another big prize, with 99 delegates that will be awarded on a winner-take-all basis on March 15. But that's getting awfully late in the primary calendar to spark momentum behind a campaign. For now, Rubio is solidly in the second tier and is looking to make a surge like it appears Cruz is doing now.

But despite what Rubio might do, or what Cruz is doing, you can't pretend Donald Trump isn't still dominating the race. Even if he doesn't retake the lead in Iowa, he's ahead in New Hampshire and South Carolina. He's also been campaigning consistently in the South.

If there was any doubt that Trump had a serious path to the nomination, it was dispelled this week by a report in the Washington Post that several top establishment Republicans, including RNC Chairman Reince Priebus, huddled in Washington to figure out what to do to stop Trump should he get to the Republican National Convention in Cleveland next summer with a sizable chunk of delegates.

At this point, it's impossible to say what would prevent that from happening. Except maybe, just maybe, it could be Ted Cruz.

