MUSCATINE, Iowa >>

Ted Cruz needs you to trust him.

Trust is the cornerstone of this fiery conservative’s campaign, which may live or die with his ability to convince voters in Iowa and across the nation that he’s the most consistent and trustworthy among the pack of White House hopefuls.

Yet as he strives for victory in Iowa’s Monday caucuses, a chorus of Republican critics led by Florida Sen. Marco Rubio is tearing at the fabric of Cruz’s message.

His GOP opponents cite a history of political opportunism they say is more in line with a used car salesman than the “consistent conservative” he claims to be. In debates, TV ads and on the campaign trail, fellow Republicans are highlighting inconsistencies in Cruz’s policies on immigration, foreign policy and even his dedication to Christian conservative values. They’re also reminding voters that the self-described outsider is an Ivy League-educated lawyer who served in former President George W. Bush’s administration.

“If you are going to campaign as the most principled, the most consistent conservative, then your record better support that,” said Rubio’s senior strategist Todd Harris. “As long as he holds himself out to be holier than thou on all things conservative, we’re going to continue to point out that he’s not.”

Cruz is betting his 2016 campaign he can win the trust argument.

The slogan, “TRUSTED”, is emblazoned on red, white and blue signs at every appearance and across the back of his campaign bus. And his closing message at debates, campaign rallies and speeches is almost always the same: “It is now up to the men and women of this great state to make the determination, who do they trust?” Cruz this week in Fenton, Iowa. “As voters, we’ve been lied to over and over and over again. The stakes are too high for us to be burned again.”

He added, “The men and women of Iowa want a consistent conservative.”

Trump, now locked in a close race for the lead in Iowa, has repeatedly called Cruz a liar in recent days. Chris Christie calls him a flip-flopper. Former Arnansas Gov. Mike Huckabee, who won Iowa’s caucus in 2008, has seized on reports that Cruz told a group of New York donors last year that he wouldn’t make fighting gay marriage a priority if elected. That’s in sharp contrast with his public promises to fight the Supreme Court’s decision.

“He’s saying one thing to a group of folks in Marshalltown (Iowa), something totally different to a group of folks in Manhattan,” said Huckabee spokesman Hogan Gidley. “Voters want someone they can trust. And it is painfully obvious at this point that Ted Cruz can’t be trusted.”

The criticism comes despite Cruz’s overwhelmingly positive ratings from conservative groups, such as the American Conservative Union, which gives him a 100 percent rating over his first two years in the Senate. In Washington, the Texas senator is often accused of being an ideological purist to a fault.

He led his party’s unsuccessful fight to strip funding from the federal health care overhaul in 2013, leading to a government shutdown. He favored a similar approach last fall in the fight to fund Planned Parenthood, but was rebuked by his party leaders still angry about his guidance two years earlier.

Now, Cruz’s own conservative purity is under intense scrutiny in the final hours before Iowa voters decide the 2016 campaign’s opening primary contest.

His competitors regularly attack Cruz’s evolutions on foreign policy, ethanol subsidies and immigration in particular. He was targeted in last week’s presidential debate by several opponents for previously supporting a pathway to legal status for immigrants in the country illegally. Cruz’s campaign suggests he wasn’t being sincere when he said in 2013 that he supported an amendment that would have granted legal status to such immigrants.

“Everybody’s for amnesty except for Ted Cruz,” said a sarcastic Kentucky Sen. Rand Paul during the debate. “But it’s a falseness, and that’s an authenticity problem.”

No one has hit Cruz harder than Rubio. The two are fighting for a role as the leading alternative to Trump as the Republican nomination contest takes off.

“People are starting to learn the truth about Ted on immigration and a bunch of other issues, and it shows a history of calculation,” Rubio said as he campaigned in Muscatine, Iowa this week. He added, “I know we’re not going to beat Hillary Clinton with a candidate who will say or do anything to gain a vote.”

Yet there is little doubt that Cruz’s conservative bona fides run deep.

He has built his campaign around the argument that he’s a “consistent conservative,” arguing that his devotion to upholding the Constitution dates back to when he memorized and recited it across Texas with a group of high school students. He also points to his record as Texas’s top lawyer, arguing nine cases before the U.S. Supreme Court.

Chris Bolvenz, a farm co-op manager from Hubbard, said he became a Cruz supporter after his 2013 filibuster trying to block funding for President Obama’s health care law — a move that led to a partial government shutdown.

“I think he’s authentic,” said the 54-year-old Bolvenz. “He’s more conservative than the other candidates.”

But it’s not hard to find Iowa voters who question Cruz’s claims.

“What frustrates me about him is that he says you’re only a purist if you’re Ted Cruz,” said Rubio supporter Benjamin Danielson, a 31-year-old hospital chaplain from Cedar Rapids. “I trust him on the major issues, but I don’t think he’s more trustworthy than anybody else.”