ONAWA, Iowa — Senator Ted Cruz of Texas insists he does not want to be seen as the front-runner in the Iowa caucuses. “The only way I know how to run is as an underdog,” he said here after a speech on Tuesday, waving off any Joe Namath-style guarantee of victory.  But try as he might to hold down expectations, Mr. Cruz has plainly become the candidate to beat in the caucuses. Barring new and damaging revelations, many Iowa Republicans now think the only thing standing between him and a victory on Feb. 1 is a groundswell of first-time or infrequent voters turning out for Donald J. Trump, of the sort that materialized for Barack Obama in 2008.  Mr. Cruz has gotten to this point by amassing an energized and growing coalition of Christian activists and anti-establishment Republicans, an extensive organization and a deep reservoir of money. But he is also benefiting from a splintered opposition that lacks either the money or the will to halt his rise.  Some supporters of Senator Marco Rubio of Florida, for example, privately say they believe Mr. Cruz cannot be defeated in Iowa. While those claims may in part be gamesmanship — an attempt to build up Mr. Cruz’s expectations here — more revealing is that neither Mr. Rubio nor the well-financed outside group allied with his campaign has so far spent money on television ads in Iowa assailing Mr. Cruz.  “It does feel like it’s now Cruz’s to lose,” said Matthew N. Strawn, a former chairman of the Iowa Republican Party.  A relatively unimpeded path has left Mr. Cruz the favorite to win the state and emerge as the preferred candidate of the party’s conservative wing. And with a dominant performance here, an unexpectedly strong showing in New Hampshire eight days later and victories in South Carolina and many of the Super Tuesday states on March 1, he could also quickly become something else: the de facto party nominee.  Mr. Cruz, obscured for much of last year by a shifting cast of attention-getting rivals, is relishing the turnabout.  Barnstorming Iowa on a six-day, 28-town campaign tour this week, he is even displaying a touch of swagger. He warns Iowans at every stop to expect tens of millions of dollars in ads attacking him to reach their TV screens and mailboxes any day now.  Joined on his 45-foot bus by a phalanx of aides and a camera crew from Showtime, and with a second motor coach carrying a swelling group of reporters, Mr. Cruz boasted about the fresh denunciations being directed his way. “I guess something has changed,” he said with barely concealed delight.  But what gives his team pause — and what is to many Iowa Republicans the crucial question leading up to Feb. 1 — is whether Mr. Trump will abruptly end his nice-guy routine with Mr. Cruz and begin attacking him in advertisements and behind the microphone at his big, highly publicized rallies.  “I’m a little concerned about that,” Representative Steve King of Iowa, Mr. Cruz’s highest-profile surrogate in the state and travel partner for part of the week, said about the possibility of a Trump offensive. “Trump is so completely unpredictable, we don’t know what he might do campaign-wise. We can’t even begin to think about anticipating that.”  Mr. Trump, whom Mr. Cruz praised for months, has begun to taunt the senator, raising questions about his Canadian birthplace and his faith. But he has stopped short of aggressively attacking Mr. Cruz and has run television commercials about only himself so far.  Mr. Cruz, responding to the birthplace slight on Tuesday, posted a video clip on Twitter from the infamous jump-the-shark episode of “Happy Days,” but has repeatedly declined to say more.  Other rivals have not given Mr. Cruz a free pass: He is coming under attack from the winners of the last two Iowa caucus votes, Mike Huckabee and Rick Santorum. Both their candidacies, which are barely registering in Iowa polls, depend on a strong result in the caucuses. But both men have little money with which to inflict damage on Mr. Cruz — and nothing like the millions that a “super PAC” supporting Mitt Romney unleashed on Newt Gingrich here in the 2012 campaign.  “They’re fighting with rocks against bazookas,” Mr. Strawn said.  Mr. Cruz has become far more entrenched in Iowa than Mr. Gingrich was at the same point in his campaign four years ago. With many conservative activists here feeling a sense of fury toward their party, Mr. Cruz has emerged as the candidate most effectively channeling the boiling anger of Republican hard-liners.  Conversations with dozens of Cruz supporters suggest that the deep dismay Iowa Republicans feel toward Washington is prompting them to coalesce behind Mr. Cruz, whom they see as the only viable conservative contender.  “We need a winner,” Susie Lee, 50, said Monday before Mr. Cruz made a late-night stop at a diner in Missouri Valley. “Huckabee and Santorum are great guys, but they haven’t been in office like Senator Cruz has, fighting.”  Pamela Oviatt of Logan, a Santorum backer four years ago, showed up before 9 p.m. for Mr. Cruz’s 10:30 p.m. appearance. She said that among activists, there was little talk of any of his rivals. “Cruz is the only one that’s in the political system now that anybody is looking at twice,” she said.  Ms. Oviatt’s distinction about Mr. Cruz’s being part of the political system remains a worrisome one for Mr. Cruz’s backers.  Iowa Republican leaders say that he is the preferred candidate among traditional activists. “He’s winning the within-the-system, anti-establishment folks,” said Don Kass, Republican chairman in Plymouth County. But the party leaders also say that Mr. Trump is garnering support from people new to the caucuses.  Indeed, Mr. Trump’s backers here say they are confident that his attacks on the political status quo will bring out thousands of Iowans who have not previously caucused or even registered as Republicans, and his campaign is trying to register supporters as Republicans.  But state party records indicate only modest increases in the numbers of registered Republicans over recent months, a pattern little different from that in previous election years. There are now just over 612,000 registered Iowa Republicans. In early August, there were just over 609,000.  The threat Mr. Trump presents has nevertheless cast a shadow of uncertainty over the caucuses and the party. And that, in its own way, has also aided Mr. Cruz: Mark Lundberg, the Sioux County Republican chairman, said he thought Mr. Cruz was one of the few candidates running who could appeal to the angry Trump legions, should Mr. Trump fall short.  Mindful of this, Mr. Cruz has seldom mentioned Mr. Trump except to praise him. This week, however, he has started invoking Mr. Trump for another reason.  Asked about attacks by some of his rivals, Mr. Cruz observed that Mr. Trump was the target of a similar barrage a few weeks ago. He also told diners at a steakhouse in Carroll to expect “tens of millions of dollars” in ads assailing him to be unleashed in the coming weeks — the sort of onslaught that a true underdog would never receive.  His eyes wandering to a political flier on a nearby table, Mr. Cruz seized on a bit of evidence. “I’m looking at a mailer some of y’all may have seen: ‘Ted Cruz is dangerous!’” he read.  “You know what? To the Washington cartel, to the career politicians there that are getting fat and happy and want the gravy train to keep going, that’s exactly right.”
The Texas senator’s campaign is building on an energized, growing coalition and a splintered opposition. Still, there’s the Trump factor to be considered.