Donald Trump and Texas Sen. Ted Cruz are circling each other in the race for the Republican nomination and appear to be on the brink of an epic clash.

While the candidates have for months observed a kind of truce, party insiders believe that’s about to change — and many are speculating about just how explosive things will get…

Mitchell McKinney, a professor of political communication at the University of Missouri, speculated that recent comments from Trump are being made with the thought that, “as we’re heading into Iowa, I’ll give the Cruz supporters something to doubt; maybe something to second-guess their choice.”…

“It’s puzzling why Trump is not going after Cruz more directly, because Cruz is a bigger threat than Trump thinks he is,” said GOP strategist Matt Mackowiak. “If Trump loses Iowa by a significant margin and then somehow loses New Hampshire … I think the whole thing falls apart. The piercing of that invincibility begins in Iowa.”

In Iowa, which holds its caucuses on Feb. 1, Ted Cruz leads Donald Trump by four points among likely caucus-goers, 28 percent to 24 percent – within the poll’s margin of error of plus-minus 4.6 percentage points. They’re followed by Marco Rubio at 13 percent and Ben Carson at 11 percent. No other Republican candidate gets more than 5 percent of the vote.

Yet among the larger universe of potential Iowa caucus-goers, Trump actually leads Cruz by two points, 26 percent to 24 percent, suggesting that a larger turnout could benefit Trump in the state. (Back in October’s NBC/WSJ/Marist poll, Trump was at 24 percent among potential caucus-goers, Carson at 19 percent, and Cruz and Rubio at just 6 percent.)

Cruz runs even with Trump among Republican voters in a head-to-head contest between only Trump and Cruz, and he leads Rubio by ten points when the two are pitted against each other.

But Trump continues to be seen by Republicans and non-Republicans alike as the party’s most likely nominee.

Donald Trump escalated his attacks on Ted Cruz’s eligibility to be president on Saturday, devoting a solid four minutes of his speech at a campaign rally here to the subject.

“[Cruz] was born in Canada,” Trump said at the Surf Ballroom here, his second of two stops today in Iowa. “Whether we like it, don’t like it, he lived there, he was there, he was born in Canada, I guess his parents voted in Canada, a lot of things, I mean a lot of things happened here. So if you’re born in Canada, it’s immediately a little bit of a problem.”…

“You can’t have a person who’s running for office, even though Ted is very glib and he goes out and says ‘Well, I’m a natural born citizen,’ but the point is you’re not,” Trump said. “You gotta get a declaratory judgment. You have to have the courts come up with a ruling. Or you have a candidate who just cannot run. Because the other side will immediately bring suit and you’ve got that cloud on your head, and you can’t have that cloud on your head.”

But if Trump’s goal is to turn voters against Cruz, there’s no evidence it’s working. It’s just not clear that this is an issue voters are particularly interested in litigating, though, unlike with the birther movement that centered around Obama during the 2008 election — and there’s just too much goodwill for Cruz here in Iowa. The same genre of attack that destroyed the likes of Jeb Bush seemingly can’t be applied to Cruz, whose supporters are much more committed and less tenuous than Bush’s.

“[Trump] goes after everybody, even poor people who have handicap issues,” said Mary Lawson, 59, before Cruz’s appearance in Sioux Center. “He says some awful things. I don’t want that as our president, can you imagine?”…

“I would care if I thought it was legitimate,” said Vickie Froehlich, 61, who drove from Minnesota to see Cruz in Pocahontas, Iowa, on Thursday. “But I don’t. And I admire Mr. Cruz, who has said he is not attacking people.”…

Trump is a “jerk,” said Nathan Lichter, 28, who saw Cruz on Wednesday night in Storm Lake. “I think he’s not nice. I think you can be conservative, be very far right conservative, and still be kind and unifying and not divisive.”

Trump reemerged as a political force on the basis of his own championing of birtherism in 2011; he allegedly bankrolled investigators who he sent to Hawaii to look into Obama’s origins, though he never released the results. Even since Obama released his long-form birth certificate, as Trump demanded, Trump has quietly continued to espouse birtherism. Given all that, it would be hard for him to not at least go through some motions on questioning Cruz’s eligibility—even if Obama had been born abroad, his mother was an American citizen, which would give him the same claim to citizenship that Cruz does. (Not that Trump has allowed a foolish consistency to be the hobgoblin of his “really smart” mind.)

Moreover, the birther attack gives Trump a good method to attack Cruz, who has recently emerged as his major rival in polling both nationally and in Iowa. But what kind of weapon is birtherism? It is, at its root, an effective way of telling voters that Cruz isn’t like them. That he’s not one of us. That he’s different. In other words, it capitalizes on all of the anti-immigrant, anti-foreigner sentiments that have driven his campaign all along…

Cruz positioned himself for months as someone similar to Trump, in the hopes that when Trump imploded (as was widely expected), he could take over Trump’s voters. Instead, Cruz has risen while Trump stays high, which means they’re still fighting for those voters. The very particular subset of voters who were susceptible to birtherism are likely also sympathetic to Trump. Emphasizing Cruz’s otherness is a good way to keep them in his camp.

Asked by “Situation Room” host Wolf Blitzer about who is tougher on immigration, Trump replied with a six-word allegation.

“Ted was in favor of amnesty,” the billionaire said.

Trump added, “Him and Marco Rubio have been fighting about who is weaker.”…

“I was watching Ted the other day and it was very interesting. He said, ‘And we must build a wall.’ OK? And my wife said, ‘Darling, he just said build a wall.’ That’s the first person that said build a wall! I’ve been saying it for five years!”

Trump continued, “He said, ‘And we will build a wall.’ So now he has taken my idea for a wall. I’m glad he has taken it, I think it’s the right thing to do. The problem is I’ll build a wall, it will be a right wall. These people, the politicians, don’t know how to build walls. They don’t know how to build anything. … But all of a sudden they are trying to come over to my territory.”

A deeper look at Cruz’s record — particularly during the divisive 2013 immigration debate — showcases how the junior senator from Texas was seeking to promote a view of immigration that could appeal to constituents in a border state transformed by an influx of migrants. A review of nearly 1,000 pages of transcripts from the five days of committee votes shows how the Texas firebrand took a nuanced view — repeatedly saying he wanted the bill to pass with several changes, especially expanded legal immigration.

“I don’t want this bill to be voted down and I hope the stakeholders who want this bill to be passed will be interested in amendments to craft a bill that will pass,” Cruz said. “And I look forward to working with the committee members in that process.”…

[A] CNN review of the committee transcripts shows that not once did he use the word “amnesty” in describing illegal immigration during the five days of lengthy deliberations, a common mantra for Cruz on the campaign trail today. And he sought to both double the cap of legal immigration from 675,000 to 1.3 million and pushed for a dramatic increase of 500% for high-skilled H-1B visas to 325,000.

When Sessions, the Alabama Republican, sought to issue stringent new caps on visas issued to foreigners from across the globe, Cruz pushed back.

Obviously, immigration is now a much bigger issue for Republican voters. It is probably now the biggest concern in the presidential primaries. Admittedly, polling says otherwise. In December, Quinnipiac found that given a list of issues, only 11 percent of Republicans picked immigration as the most important one. But I think looking at those polls alone underestimates its importance. I submit that conservatives are now starting to see a candidate’s position on immigration as an index of his conservatism in general.

Abortion politics followed a similar trajectory. Opposing abortion wasn’t always considered part and parcel of conservatism. Everybody considered Senator John Tower of Texas a movement conservative even though he supported legal abortion. Over time, though, as conservatives grew more opposed to abortion and liberals more supportive of it, it became an issue that voters used to sort candidates by ideology…

Today, favoring tighter control of immigration is becoming a stand-in for conservatism in the same way. What that means exactly is a little hard to say. But the same was true in the case of abortion. Could a politician be considered “pro-life,” and thus have that conservative credential, if he favored keeping abortion legal in cases of rape and incest? Over time it became clear that yes, he could. A politician could also meet the test even if he showed no burning passion to fight abortion. If, on the other hand, a politician said it should generally be legal but not taxpayer-funded, he wouldn’t meet the test…

The new political line-up doesn’t mean that a Republican presidential candidate will have to embrace the emerging conservative orthodoxy to get the nomination. Rubio could win even if opponents of his immigration record successfully define him as an “establishment” candidate. After all, parties usually nominate establishment candidates. But the winner will have to deal with the new political reality: A hard line on immigration, however it is defined, is now part of the conservative creed.

“Hav­ing Steve King up there speaks volumes for his cred­ib­il­ity,” said New Hamp­ton res­id­ent Jane Collins after that town’s event. “Im­mig­ra­tion is very im­port­ant. There’s people liv­ing here and get­ting be­ne­fits that we’re pay­ing for that they’re not pay­ing taxes or any­thing. It’s tak­ing away from those work­ing hard and that maybe have had set­backs and have been less for­tu­nate.”…

Fol­low­ing Sat­urday’s event in Oel­wein, Betty Miller, an In­de­pend­ence, Iowa, res­id­ent, said that King “is a hero in Iowa,” es­pe­cially for his po­s­i­tion on im­mig­ra­tion. To her, Trump made im­mig­ra­tion a cam­paign is­sue for this elec­tion, but Cruz can con­tin­ue the de­bate.

“Trump is do­ing so well be­cause he stood up and put it out there,” she said. “When Trump brought it out, Cruz stepped up to the plate. We like people who don’t back down. Cruz is real and he really has a heart.”

These are not one-is­sue voters. When Cruz men­tioned his plans to over­turn Obama’s ex­ec­ut­ive or­ders on gun con­trol and have the De­part­ment of Justice in­vest­ig­ate Planned Par­ent­hood, crowds on Sat­urday ap­plauded loudly, whist­ling and cheer­ing. But in a state that has a grow­ing Latino pop­u­la­tion that threatens the norm of small towns, im­mig­ra­tion is on the short list of is­sues that can determine who voters go out and caucus for on Feb­ru­ary 1.

Cruz, who spent much of 2015 gushing about how “grateful” he was for Trump’s contribution to the immigration debate, has decided to attack Trump as a supporter of amnesty. This is a few things. First, it’s amazing. Trump, who has gone so far as to call for a ban on Muslims’ entry into the country, will now be portrayed as insufficiently “tough” on immigration. It’s also a nice check of how far Cruz, in his effort to keep up with (and now surpass) Trump’s rightward lunge on immigration, has moved to the right on this issue in the past year. When Cruz entered the race, he was already far right on immigration. He has since moved further, rejecting even the slimmest possibility that he might consider a plan granting legal status to undocumented immigrants, as well as renouncing his previous support for increasing legal immigration levels for skilled workers. Trump and Cruz both support eliminating birthright citizenship, too, for what it’s worth…

It’s going to get much worse if Trump and Cruz end up fighting against each other for the largest chunk of the electorate down the stretch. Cruz has indicated that he will jump to Trump’s right on immigration, which will likely cause Trump to move to his own right, against any eventual legal status, to maintain his anti-immigration base. From there, the two leading candidates for the nomination will have taken extremely severe positions against immigration reform, though they will bicker about how the other is weak nevertheless. And so the race to the bottom extends for several more months.

This is a hackneyed observation, but I’m going to make it again because it tickles me: Imagine telling the RNC in 2013, when its “autopsy” of the 2012 election stated that the party must champion comprehensive immigration reform in order to win the presidency, that the nomination would likely come down to Donald Trump and Sen. Ted Cruz, and that it would be fought over immigration and who can take the most rejectionist stance.

“The chickens have come home to roost,” Mr. Buchanan said. “Putting the party back together again will be very hard after this nomination race. I think the party is going to shift against trade and interventionism, and become more nationalist and tribal and more about protecting the border.”…

“If Trump or Cruz wins the White House, then my side of the party has to re-evaluate who we are, what we stand for, and I’d be willing to do that,” Mr. Graham said. “But if Trump or Cruz loses the presidency, would their supporters re-evaluate their views on immigration and other issues that would grow the party? If they do that, we can come back together. If they don’t, the party probably splits in a permanent way.”…

The presidential historian Richard Norton Smith, who has written biographies of some of the 20th century’s leading Republicans, said a nomination of Mr. Trump would represent “a hostile takeover” of the party, and make it more difficult for old-guard party leaders to suppress the passions of a more hard-core, anti-immigration, angry base.

“The nativists aren’t going away,” Mr. Smith said. “They might, if anything, become more feverish.”