By Steve Holland
WASHINGTON (Reuters) - Republican front-runner Donald Trump looked to Arizona and Utah on Tuesday to add to his big lead in the party's presidential nominating race in what would be another blow to an anti-Trump movement organized by establishment Republicans.
The contests in Arizona and Utah were overshadowed by attacks in Brussels that left at least 30 people dead, and added to security concerns that American voters have expressed to pollsters.
"I have proven to be far more correct about terrorism than anybody - and it’s not even close. Hopefully AZ and UT will be voting for me today!" Trump, who was monitoring the results from Florida, said in a tweet.
Trump, the New York billionaire and former reality TV star, has ridden an anti-Washington message to become the favorite for the nomination. This has left a flagging anti-Trump effort with faint hopes of stopping him at the Republican national convention in July.
In Arizona, which is one of the U.S. 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.
Arizona will award its entire slate of 58 delegates to the winner of Tuesday's primary. In Utah, the state's 40 delegates will be awarded proportionate to the popular vote, unless a single candidate captures at least 50 percent of the vote, in which case that person will be awarded all the delegates.
On Monday, Trump warned against efforts to deny him the nomination if he falls short of securing the 1,237 delegates needed ahead of the July convention. Trump now has 678 delegates.
"I think it is going to be very hard for them to do," Trump said on CNN of any effort to deny him the nomination if he falls short. "I have millions of votes more than anybody."
Democrats were also voting on Tuesday, in Arizona, Utah and Idaho, with front-runner Hillary Clinton aiming to pile up more delegates in her race against challenger Bernie Sanders.
Sanders, a U.S. senator from Vermont, is looking for wins in many of the six Democratic contests this week. Alaska, Hawaii and Washington will vote on Saturday. But because Democratic delegates are awarded proportionally in all states, Clinton will keep adding to her delegate total even if she is not the winner in a given state.
Tuesday's Republican contests are the first since U.S. Senator Marco Rubio of Florida dropped out a week ago after Trump drubbed him in his home state. Ohio Governor John Kasich is the only other candidate still in the race, splitting the anti-Trump vote with Cruz.
"We welcome Marco's supporters with open arms," Cruz said on CNN, saying a Trump candidacy in November would be "a disaster" that would ensure a Clinton win.
In Arizona, Trump had the backing of former Republican Governor Jan Brewer and Maricopa County Sheriff Joe Arpaio, two of the most prominent supporters of a crackdown on illegal immigrants.
In Utah, Mitt Romney, the 2012 Republican presidential nominee, has said he will vote for Cruz.
Romney recorded phone messages on behalf of Cruz, saying, "He is the only Republican candidate who can defeat Donald Trump" and that a vote for Kasich was equivalent to a vote for Trump.
(Additional reporting by John Whitesides; Editing by Leslie Adler)