Primary poll hours, results (3/22/16): Arizona, Utah, Idaho

In Arizona, which is one of the USA states that borders Mexico, Trump's hardline immigration message is popular and he leads in polls, while in Utah Trump lags in polls behind top rival Ted Cruz, a U.S. senator from Texas.

Republican leaders adamantly opposed to Donald J. Trump's candidacy are preparing a 100-day campaign to deny him the presidential nomination, starting with an aggressive battle in Wisconsin's April 5 primary and extending into the summer, with a delegate-by-delegate lobbying effort that would cast Mr. Trump as a calamitous choice for the general election. "At this point", Romney said on the call, "a vote for John Kasich is a vote for Donald Trump". The candidate who can win Utah by more than 50 percent will walk away with all 40 delegates.

The CBS News/New York Times national poll also conducted March 17-20 similarly has Trump in the lead at 46%, followed by Cruz at 26% and Kasich at 20%. But Mitt Romney, the former MA governor and 2012 Republican nominee who is a Mormon and votes in Utah, said he'll caucus for Cruz on Tuesday night. The other candidate in the race, John Kasich, has 143 delegates so far.

Recognizing that Mr. Trump has seized a formidable advantage in the race, they say that an effort to block him would rely on an array of desperation measures, the political equivalent of guerrilla fighting.

Can Sanders get his momentum back?

The contests are important tests for Sanders, who one week earlier lost five big-state contests to Clinton and has long argued he can run up delegate advantages when the campaign moved West.

He's looking to cut into front-runner Hillary Clinton's delegate lead in a state where she was soundly defeated by Barack Obama in 2008.

And he's arguing that Republican-leaning Western states are the place to do it. "I believe it would be a disaster for our party", said Oeftering. Utah has 37 Democratic delegates.

If she can keep Sanders from catching up, she can keep her focus on attacking Trump - instead of the Democratic contest.

"At this stage, the only way we can reach an open convention is for Senator Cruz to be successful in as numerous remaining nominating elections as possible", Romney said on Facebook on Friday.

Asked whether Trump would behave differently as president, Clinton answered, "Who knows?"