WASHINGTON (AFP) - The race for the White House shifted westward on Tuesday (March 22) as voters in Arizona, Utah and Idaho make their picks in a narrowing presidential contest dominated by Republican Donald Trump and Democrat Hillary Clinton.
The voting gives the candidates another opportunity to pile up delegates on the way to the party nominating conventions, but is not expected to alter the basic outlines of the race.
The deadly attacks in Brussels changed the tone of voting day from the start, with Mr Trump and his main rival Ted Cruz seizing the moment to bash President Barack Obama's foreign policy - and tout their own tough stances on immigration.
Anyone who tries to attack the United States will "suffer greatly," Mr Trump said, in typically blunt tones that have shaped his populist run for the White House, propelling him from outsider to firm favorite for the Republican ticket.
"Belgium is a horror show right now. Terrible things are happening," he said.
"We have to be very careful in the United States. We have to be very, very vigilant as to who we allow into this country."
At stake are 98 delegates in the Republican contests in Arizona and Utah, and 131 for Democrats who, unlike the Republicans, also caucus in Idaho.
At this point in the Republican race, Mr Trump's main objective is to amass the 1,237 delegates needed to win his party's nomination outright, and thwart a bid by the party establishment to stop him.
Going into Tuesday's contests, the billionaire real estate mogul had 683 delegates to 421 for his nearest rival, Senator Cruz of Texas, according to a CNN tally. Ohio Governor John Kasich has 145.
Pre-election polls show Mr Trump heavily favoured to prevail in winner-take-all Arizona, the biggest prize with 58 delegates.
The south-western border state has long been roiled by passions over immigration, an issue Mr Trump has seized on since launching his campaign with inflammatory accusations that Mexico was sending rapists and criminals across the border and his promise to build a border wall.
Mr Trump touts endorsements from Maricopa County Sheriff Joe Arpaio, himself a magnet of controversy for policing practices that target immigrants, and ex-governor Jan Brewer, who championed a state crackdown on undocumented migrants.
Anti-Trump protesters blocked a major road near Phoenix on Saturday and Mr Trump supporters at a Tucson rally kicked and punched a protester.
Mr Trump defended his campaign manager Corey Lewandowski, who appeared to have collared a protester in the middle of the Tucson melee.
"I give him credit for having spirit," he said on ABC's "This Week." The dynamics are different in neighboring Utah, a predominantly Mormon state where pre-caucus polls show the ultra-conservative Mr Cruz positioned to win.
Mr Cruz has been given a boost by Mr Mitt Romney, the losing 2012 Republican nominee who has led the charge to stop Mr Trump.
Utah is home turf for Mr Romney, a Mormon from a prominent family who has encouraged Utah residents to vote for Mr Cruz.
Analysts note that Mormons have voted consistently against Mr Trump elsewhere. The Church of Jesus Christ of Latter-day Saints, breaking with the view of many Republicans, has supported immigration reform.
Utah's 40 Republican delegates are all up for grabs by any candidate who wins a majority in the state caucuses.
Mr Cruz's biggest Utah obstacle may not be Mr Trump but Mr Kasich, who has refused entreaties from Mr Romney and others to stay out of the race to give Mr Cruz a clearer shot at taking all the delegates.
"I'm going to compete across the country and tell people who I am and let the chips fall where they may," Mr Kasich told NBC Sunday.
"And let me also tell you, no one, no one is going to that convention with enough delegates."
On the Democratic side, Mrs Clinton is dogged by an unyielding opponent in Mr Bernie Sanders, whose well-funded grassroots campaign is going strong despite a string of losses and the former secretary of state's growing pile of delegates - 1656 to his 877, including super-delegates, according to CNN.
To win the Democratic nomination, 2,383 delegates are needed.
Pre-election polls show Mrs Clinton with a double-digit lead in Arizona, boosted by Hispanic support and a closed primary system that may not favor Sanders and his independent supporters.
Mr Sanders has pointed to a recent national CNN poll that shows him topping all three Republican candidates in head-to-head matchups. Mrs Clinton leads Mr Trump, runs even with Mr Cruz and trails Mr Kasich according to respondents.
"There is no question that you are looking at the strongest Democratic candidate," Mr Sanders tweeted.
He is expected to do better in Utah and Idaho, states with predominantly white populations. But there has been little polling in either state, making the outcome uncertain.