(AP) -- From sounding duck calls to predicting the weather, presidential contenders are blanketing Iowa in a final frenzy to close the deal before Monday's Iowa caucuses begin the formal process of choosing President Barack Obama's successor.

Republican Donald Trump, campaigning with his wife, Melania, and pregnant daughter, Ivanka, continued his attacks on Texas Sen. Ted Cruz. The two men lead polls of likely caucus-goers. Trump also predicted that "many" senators would "soon" endorse him rather than their Texas colleague. Trump didn't name any such senators, and none immediately emerged.

Cruz, meanwhile, campaigned on the eve of the caucuses with conservative media firebrand Glenn Beck and "Duck Dynasty" cable TV star Phil Robertston.

Florida Sen. Marco Rubio, who is running third, pitched himself as the pragmatic choice for Republicans who want to win in November.

In a deadlocked Democratic race, Hillary Clinton stuck to her message that she's the most experienced and most electable candidate, as she tries to stave off insurgent candidate Bernie Sanders.

The Vermont senator looked to build on his apparent momentum, as he appeared before enthusiastic crowds the same afternoon that his campaign announced it raised more than $20 million in January, a sign that he will continue to match Clinton's considerable resources.

One development -- the weather -- was beyond the candidates' control. Snowfall forecast to start Monday night appeared more likely to hinder the hopefuls in their rush out of Iowa than the voters going to caucus. Republican John Kasich already has decamped to New Hampshire.

Iowa offers only a small contingent of the delegates who will determine the nominees, but the game of expectations counts for far more than the electoral math in the state. Campaigns worked aggressively to set those expectations in their favor for Iowa, the Feb. 9 primary in New Hampshire and beyond.

The one agreement among all candidates: The outcome will boil down to turnout, and they're trying to make whatever argument they can to ensure their supporters, perhaps, a few last-minute deciders, show up on Monday night.

At an afternoon rally in Iowa City, Cruz urged voters to bring 10 of their friends to caucus on Monday. "We can't roll the dice," he said.

Joined by Robertson, patriarch of the "Duck Dynasty" clan from Louisiana, Cruz sounded a duck call usually reserved for hunting. The senator sounded the symbolic call for a "one-on-one" debate with Trump, which he pitched when Trump skipped the final debate held Thursday in Des Moines.

Robertson, an outspoken religious and social conservative, told the crowd that "depravity" and "perversion" grip the nation, and that Cruz is the antidote. "Cruz trusts God," Robertson said. "Cruz trusts James Madison. That's why I trust Cruz.

The argument is aimed at evangelical Christians who could make up the majority of the GOP caucus-goers.

Trump made his own religious play earlier Sunday, starting his day attending a mass outside Des Moines, at about the time taped interviews on Sunday talk shows aired in which the billionaire businessman continued his verbal assault on Cruz.

He's questioned Cruz's eligibility to be president because of his Canadian birth and framed his as a tool of big banks, despite Cruz's efforts to campaign as an anti-establishment conservative. Continuing Sunday afternoon, Trump hammered Cruz for sending some Iowa voters a mailer that suggests they have committed a "voting violation" for poor participation in past presidential caucuses.

"It is so dishonest. It is so dishonest," Trump said in Council Bluffs.

Cruz has called the mailers "routine."

On the airwaves, Cruz focused his final offensive on Rubio. One ad says the Florida senator is the candidate of "tax hikes" and "amnesty" and described him as "the Republican Obama."

Rubio has taken his own shots, particularly as he and Cruz joust over who is more conservative on immigration. But the Florida senator also tries to position himself above the fray, arguing he's the best hope for Republicans to defeat the Democratic nominee in November.

At Northern Iowa University on Sunday, Rubio suggested "policy differences are not enormous" among GOP hopefuls, leaving voters to decide "who gives us the best chance" in a general election. "Think about that for a moment," he said, "because we can't lose. ... This election has to be about the future."

Among Democrats, Clinton made similar arguments to those she offered during her failed 2008 White House run, as she tried to cap Sanders' gains. "Stick with me," she urged backers Sunday in Council Bluffs. "Stick with a plan, stick with experience."

Earlier Sunday, Clinton said on ABC's "This Week" that she's been subjected to "years of scrutiny, and I'm still standing." She added, "I feel vetted ... and I think I'm the best person to be the nominee and to defeat whoever they nominate in November."

Sanders essentially embraced that framing Sunday in Marshalltown, Iowa, as he implored young and disaffected voters to help him mount "a political revolution."

Sanders said the campaign isn't just about his policy positions like making the wealthy pay a fairer share in taxes, demanding a $15 an hour minimum wage, pay equity for women and better trade policies. "It is about revitalizing American democracy," he said, "That's what you're doing here.

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Barrow reported from Atlanta. Associated Press writers Steve Peoples, Lisa Lerer, Catherine Lucey, Scott Bauer, Tom Beaumont and Ken Thomas in Iowa, and Julie Bykowicz in Washington contributed to this report.