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DES MOINES, Iowa – The race to win the Iowa caucuses turned even more sharply combative Sunday as candidates desperate for an edge dashed through a frenzied final day of campaigning.

Donald Trump, standing on the verge of a potentially stunning victory on Monday night called his Republican rival Ted Cruz a “liar” and made a play for the Texas senator’s evangelical power base. Cruz questioned his rival’s conservative authenticity on abortion and religious liberty and appeared alongside Duck Dynasty’s Phil Robertson, who branded same sex marriage “wicked” and “evil.”

Democrat Hillary Clinton, meanwhile, clung to an inside-the-margin-of-error advantage over Bernie Sanders as she battles to bottle up the self-described democratic socialist before he becomes a genuine threat to capture the nomination. Sanders complained he could not keep up with distortions of his record by the Clinton camp while a former aide to President Barack Obama took to Twitter to accuse the Vermont senator of repudiating their old boss’s record.

The final shots underscore how close the Iowa contest is for both parties. The final Des Moines Register/Bloomberg Politics poll on Saturday night, which has often been an effective barometer of how the race eventually shakes out put Trump on top of Cruz 28% to 23% with Sen. Marco Rubio in third at 15%. Clinton, hitting her stride on the stump in recent days, leads Sanders 45% to 42%.

These first-in-the-nation votes will not decide the nomination — there are only a tiny fraction of the required delegates at stake — but they are likely to winnow down the GOP field and set expectations for the bigger state primaries that lie ahead.

The caucuses are crucial for Trump because they will be the first true test of his strength. Will he be able to turn the anger he has whipped up against GOP elites into votes? Or will Trump’s lashing of Muslims, Mexicans and his rivals turn off voters eager to select a nominee who can beat a Democrat in the fall and who fits a more traditional mold as commander in chief?

Driving home his advantage Sunday, Trump laid into Cruz, taking exception to claims by the Texas senator that he would save President Barack Obama’s signature health care law if he made it to the White House.

“Look, Ted Cruz is a total liar. I am so against Obamacare. I’ve been saying it for two years in my speeches, I’m going to repeal and replace Obamacare,” Trump said on ABC’s “This Week.” “I don’t even know where he gets this.”

Trump, hoping to influence religious voters who play a key role in Iowa, went to church with his wife Melania on Sunday. The billionaire swayed in time to the hymns at First Christian Church in Council Bluffs and took communion.

And seeking to peel away any wavering evangelicals from Cruz, Trump also linked up with Jerry Falwell, a hero of the Christian right, who endorsed him despite skepticism among some believers about the depth of Trump’s faith.

Cruz is under intense pressure to deliver a victory on Monday night since Iowa is a state perhaps most receptive to his appeal to ideological conservatives and evangelicals. A defeat would cast doubt on his wider appeal in the delegate-rich southern states he hopes could pave the way to the nomination.

With that in mind, Cruz on Sunday drew a firm contrast between his ideology and that of Trump.

“I do think policy differences are fair game,” Cruz told CNN’s Jake Tapper on “State of the Union.”

“He and I have very, very different views on questions like life and marriage and religious liberty. He and I have very, very different views and records on questions like health care and Obamacare and amnesty.”

Making his closing argument to voters in Iowa City where he campaigned with conservative broadcaster Glenn Beck and Robertson of A&E’s “Duck Dynasty,” Cruz urged voters to ignore the media surrounding the presidential race and get out to caucus on Monday night. Evidence of his ground game was in full effect outside where volunteers spread out at long tables collecting information from voters willing to caucus tomorrow.

He sought to differentiate himself from Trump by telling voters that if they were looking for someone who could “maybe make some deals, I ain’t your guy.”

Honing his argument that he is the true conservative in the race, he also implied that a vote for Trump was a risk.

“This is your time to make the decision for the men and women of Iowa to say we can’t get fooled again,” he said to a crowd of several hundred people who crammed into one of the exhibition halls at the state fairgrounds in Iowa City. “The stakes are too high. We can’t roll the dice.”

Cruz also drew fire from his other flank, as Rubio seeks at least a good third-place finish to make the case that he is a stronger alternative to Cruz and Trump than ex-Florida Gov. Jeb Bush, New Jersey Gov. Chris Christie and Ohio Gov. John Kasich.

“This whole notion Ted has that he’s the only conservative, I think as people learn more about his record, they’ll realize what he really (is) is very calculating,” Rubio told Tapper.

“He’s always looking to take whatever position it takes to win votes or raise money, and we’re not going to beat Hillary Clinton with someone that will say or do anything to get elected,” Rubio said.

Clinton on Sunday geared up for an anxious wait to see whether the turnout machine she built while learning lessons of her 2008 caucus defeat to Obama will counter the wave of increasing enthusiasm for Sanders.

But she was dogged by questions about the private email server she used while secretary of state, which is under investigation by the FBI to see whether any classified information was illegally compromised.

“It was not the best choice,” Clinton said, admitting on “This Week” that using a government email account would have spared her political pain.

“I wouldn’t be here talking to you about it,” she said. “I’d be talking about what people in Iowa are talking to me about, about affordable health care and jobs and rising wages and all of the concerns that are on their minds.”

Sanders stuck to his vow not to use the email issue against Clinton but did accuse her campaign of turning negative against him.

“I can’t keep up with what the Clinton campaign does, to be honest with you,” Sanders said on “State of the Union.”

Still, inside Clinton’s campaign, there was quiet optimism that her get-out-the-vote effort would yield victory on Monday night.

“We’ve had an amazing grass-roots organizing effort,” Clinton told CNN on Saturday. “I’m so proud of all the people who have put it together and the, literally, tens of thousands of volunteers that they’ve enlisted.”

The Clinton campaign has 4,200 precinct captains and other precinct leaders prepared for Monday night. By Sunday, according to aides, campaign volunteers will have knocked on 125,000 doors this weekend alone.

Former President Bill Clinton, meanwhile, took aim at politicians who he implied did little more than voice the frustration of voters. It appeared to be a jab at Sanders, who has inspired legions of rank-and-file Democrats with his broadsides against Wall Street and an economy he says is skewed toward the wealthy.

“When you’re angry and frustrated, the typical thing to do — and it’s so emotionally satisfying for about 30 seconds — is to label and blame, label and blame, label and blame,” Clinton told a historic black congregation in Des Moines.

“This church was not built on label and blame,” he said. “This church was built on people taking responsibility.”

Obama’s former political guru David Plouffe, who has endorsed Clinton, meanwhile warned on Twitter that Sanders was embracing the concept of buyer’s remorse over the president.

“Sanders closing with Cornel West and embracing idea of Buyer’s Remorse with @POTUS. Be honest then Senator – run firmly against Obama record,” Plouffe tweeted.

Like the Clinton campaign, Sanders also touted his Iowa organization, saying on “State of the Union” that he would have 15,000 volunteers knocking on doors in Iowa and making phone calls on his behalf.

“All I know is, we are bringing out large numbers of people,” he said. “We’re creating a lot of excitement and energy on the part of people who really are tired of establishment politics and establishment economics.”