Arizona and Utah feature contests for both parties, while Idaho Democrats also hold presidential caucuses. Trump and Clinton hope to strengthen their leads in delegates that decide the nominations, as Democrat Bernie Sanders and Republicans Ted Cruz and John Kasich struggle to reverse the sense of inevitability taking hold around both party front-runners.

Read more: Caucus night approaches: What to know

“I have more votes than anybody,” Trump charged on the eve of the elections as he courted skeptical Republican officials in the Washington. “The people who go against me should embrace me.”

A firm delegate lead in hand, Clinton looked past Sanders ahead of Tuesday’s contests and instead sharpened her general election attacks on Trump. “We need steady hands,” she said, “not a president who says he’s neutral on Monday, pro-Israel on Tuesday and who-knows-what on Wednesday because everything’s negotiable.”

Despite the tough talk, both Trump and Clinton face challenges on Tuesday.

Trump’s brash tone has turned off some Republican voters in Utah, where preference polls suggest Cruz has a chance to claim more than 50 percent of the caucus vote — and with it, all of Utah’s 40 delegates. Trump could earn some delegates should Cruz fail to exceed 50 percent, in which case the delegates would be awarded proportionally based on each candidate’s vote total.

Kasich hopes to play spoiler in Utah, a state that prizes civility and religion. A week ago, the Ohio governor claimed a victory in his home state — his first and only win of the primary season. Yet Mitt Romney, the GOP’s 2012 presidential nominee, is telling his fellow Utah voters in a recorded phone message that Cruz “is the only Republican candidate who can defeat Donald Trump.”

Kasich has invested heavily in Utah in recent days, airing $215,000 in ads, including an online-only ad that falsely implies Romney backed him, rather than Cruz, in Utah. Romney, whose primary goal is stopping Trump, supported Kasich in Ohio.

Trump appears to be in a stronger position in Arizona. Cruz’s team has been aggressively lowering expectations in that state, which will award all of its 58 delegates to whichever candidate wins the most votes.

Anti-Trump Republicans are running out of time to prevent the billionaire businessman from securing the 1,237 delegates needed to claim the nomination.

With more than half of all delegates already awarded during the first seven weeks of primary voting, Trump’s challengers’ best — and perhaps only — hope lies with denying the front-runner a delegate majority and forcing a contested national convention in July.

“This is going to the convention,” Kasich said Tuesday night on CNN.

On the Democratic side, Clinton’s advantage is even greater.

The former secretary of state is coming off last week’s five-state sweep of Sanders, who remains popular among his party’s most liberal voters but needs to improve his performance if he expects to stay relevant. The Vermont senator, now trailing Clinton by more than 300 pledged delegates, has targeted Tuesday’s races as the start of a comeback tour.

Clinton, it appeared at times Tuesday, had already moved on. Campaigning in Phoenix, she took aim at Joe Arpaio, the sheriff in the county that includes Phoenix who made his name by chasing down people who are in the country illegally. Arpaio is a vocal Trump supporter, and Clinton called him and others out for “treating fellow human beings with such disrespect.”

“I don’t ever remember anything like it,” she said. “You know pitting groups of Americans against each other, it just is wrong.”

Written by STEVE PEOPLES, Associated Press; Associated Press writer Catherine Lucey in Phoenix contributed to this report.

Follow Steve Peoples on Twitter.