Texas Sen. Ted Cruz walks out of a campaign event at the Heartland Acres Agribition Center on a snowy Monday in Independence, Iowa. (Joe Raedle/Getty Images)

Ted Cruz, who established himself as Iowa’s prohibitive favorite in early January with an intimidating show of force, is suddenly under siege one week before the caucuses as rival Republicans pummel him and as opposition to his presidential candidacy from the state’s political and business elite hardens.

Although Cruz is campaigning aggressively, his advisers are concerned about the barrage and are now scrambling to reset expectations for him here. They insisted Monday that the senator from Texas always has been the “underdog” in Iowa and argued that a second-place finish to Donald Trump should be interpreted as a mark of grit and would catapult him onward in the nominating contest.

“I can’t guarantee we’ll win,” Cruz told a group of pastors Monday at a private meeting in Cedar Rapids. “I don’t know that. That’s out of my hands. I believe we have a path to victory.”

Still, a loss in Iowa — the state where Cruz has campaigned the most and where the GOP’s deeply conservative base seems a natural fit — would call into question the depth of his coalition. Also at stake is the credibility of his vaunted data and field operation, which in Iowa is believed to be more sophisticated than any other Republican’s.

Cruz’s standing for weeks atop many Iowa polls has thrust him into the crosshairs. Trump is hitting him relentlessly over his Canadian birth and his “nasty” reputation in Washington, while using the endorsement of former Alaska governor Sarah Palin to drive a wedge with evangelicals. Sen. Marco Rubio (Fla.) is portraying Cruz as a calculating politician and proponent of European-style economics. Fellow religious-

conservative candidates Mike Huckabee and Rick Santorum are charging that he is a fraud.

Republican presidential candidate Donald Trump continued to question Canadian-born opponent Ted Cruz's eligibility to run for president at a campaign event in Farmingham, N.H., on Jan. 25. (Reuters)

What’s more, Iowa’s powerful ethanol industry is going all-out with an anti-Cruz campaign. Longtime Gov. Terry E. Branstad broke his usual neutrality by calling for Cruz’s defeat over the issue. Iowa’s two U.S. senators, Charles E. Grassley and Joni Ernst, both Republicans, are also showing favoritism for Trump and Rubio, respectively, while a man dressed in a Royal Canadian Mounted Police uniform trailed Cruz over the weekend.

[Here’s how the Iowa caucuses work]

“Welcome to the big time, baby,” said Tim Albrecht, a former Branstad aide who is advising former Florida governor Jeb Bush’s campaign. “You put your head out there, it’s going to get lopped off. That’s exactly what’s happening.”

For Cruz, the moment is perhaps the greatest test of his celebrated career. Most comfortable on the offensive, he is now forced to absorb the strikes.

“If Donald wins Iowa, he right now has a substantial lead in New Hampshire,” Cruz said at the pastors meeting. “If he went on to win New Hampshire as well, there’s a very good chance he could be unstoppable and be our nominee. And the next seven days in Iowa will determine whether or not that happens.”

Cruz is trying to bolster his profile as a maverick conservative, lobbing shots at the “establishment” and pegging Trump — his top competitor here — as an untrustworthy chameleon. The escalating tension will come to a head Thursday night on Fox News Channel in the final debate before Monday’s caucuses.

“There are a lot of forces aligned against us,” Cruz spokesman Rick Tyler said. “We have never said we expected to win Iowa. We would of course be grateful if we did, and it would be a real boost to our campaign, but again, we’re the underdog in the race.”

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Bob Vander Plaats, an Iowa evangelical leader and one of Cruz’s national co-chairmen, said he “didn’t expect this much of an onslaught.”

“There is a lot of incoming,” Vander Plaats said. “But I think he should take it — all of it — as a badge of honor.”

Cruz led Trump in Iowa, 25 percent to 22 percent, in a Jan. 13 Des Moines Register-Bloomberg Politics poll, though more-recent surveys show Trump moving up. A Fox News poll released Sunday shows Trump leading Cruz, 34 percent to 23 percent.

Meanwhile, Rubio, who has been running third here, has had some victories. The Des Moines Register just endorsed him, while Ernst appeared with him and offered glowing remarks Monday, though she said she was not formally endorsing.

Joseph Brown, a pastor from Washington, Iowa, said he and other Cruz supporters are worried. “If Trump does win and Cruz comes in second — or even a close tie — it’s going to embolden the Trump phenomenon to the point where it’s going to really damage, I think, the momentum of Senator Cruz,” Brown said. He went on to call Trump “an in­cred­ibly wicked man.”

Cruz’s campaign is going after Trump in ads, including one painting him as a heartless taker of a widow’s property through his company’s use of eminent domain. Another, released Monday afternoon, skewers Trump for “New York values,” highlighting his 1999 support for abortion rights and same-sex marriage. That message is amplified by an ad from Cruz’s allied super PAC.

Trump is hitting back in his own spots, including one mocking Cruz for stammering in an interview over immigration.

Further compounding problems for Cruz are Huckabee and Santorum, winners of previous caucuses. They are polling in the low single digits here but are positioned to siphon off support from Cruz because they appeal to a similar demographic.

[GOP establishment warms to Trump — and remains cool to Cruz]

Tensions have long simmered between Cruz and Huckabee, and the former Arkansas governor has painted him as a compromising shape-shifter.

Huckabee is also developing a friendship with Trump. On Jan. 6, the two men spoke by phone and talked politics, aides to the candidates confirmed.

“He’s great. I’ve liked him since Day One. Warm. Good man,” Trump said in an interview. Referring to Huckabee and Santorum, Trump said: “I hope they do well, I honestly do. If they get out for some reason, I’d love to have their endorsement.”

The animus toward Cruz extends to the faith-infused campaign of Ben Carson, who briefly led the Iowa polls last year but has since fallen into the second tier. Cruz’s Iowa rise was fueled in part by defections from Carson, but Carson intimates are openly hostile toward the Texan.

“Poaching voters from Dr. Carson? Please,” said Armstrong Williams, a Carson confidant.

Cruz asserted himself as the candidate to beat in Iowa the first week of January with a six-day, 28-stop bus tour through the state’s far-flung areas. “He was making real inroads with good, solid, conservative Republican activists,” said Matt Strawn, a former state GOP chairman.

This seemed to awaken the state’s establishment. Cruz’s vow to phase out the renewable-fuel standard alienated the powerful ethanol industry here, which relies on the federal subsidy.

Branstad, an industry advocate, said last week that a Cruz win would be “very damaging” for Iowa. He doubled down Monday on his comments. The governor’s son, Eric, runs an ethanol lobby group that has been attacking Cruz.

“The establishment has made its decision. They need to demonize somebody over ethanol, and they’ve decided to make that person Ted,” said Rep. Steve King (R-Iowa), a top Cruz surrogate.

King added: “The other day I went online and saw a picture of Governor Branstad wearing a ‘Make America Great Again’ hat with one of Trump’s sons. That told me all I needed to know.”

Grassley appeared at a Trump rally Saturday in Pella and echoed many of the mogul’s signature phrases. Jeff Kaufmann, the state GOP chairman, spoke effusively about Trump at a rally the next day.

On the campaign trail, however, there is a contrary narrative. Cruz held two large, boisterous rallies Saturday where he accepted the endorsement of media personality Glenn Beck. In a show of confidence, Cruz held up his right hand and took a mock oath of office.

Michael Demastus, a Des Moines-area pastor who delivered the blessing at one of the events, said he found the crowd invigorating.

“They’re with Ted,” he said of evangelical voters, “locked up.”

Katie Zezima in Cedar Rapids, Iowa, contributed to this report.