The Note: Primary Primer

— -- NOTABLES

The Brussels attacks are dominating the news, but tonight three states out West vote in Tuesday’s primaries and caucuses. Both Republicans and Democrats are participating in the Arizona primary and the Utah caucuses, while only Democrats in Idaho will caucus today. Here are several things to watch in Tuesday’s primaries, courtesy of ABC’s VERONICA STRACQUALURSI and PAOLA CHAVEZ:

--HOW WILL TRUMP FARE IN ARIZONA AND UTAH? The Grand Canyon State is Tuesday’s big prize as a candidate could win all 58 available delegates. Donald Trump looks well positioned there. He has the backing of former Arizona Gov. Jan Brewer and Sheriff Joe Arpaio, the man who oversees the controversial “Tent City” jail. However, in Utah, Trump may have a harder time wrangling voters to his side, after insulting Mitt Romney, a Utah resident. “Are you sure he’s a Mormon?” Trump said of Romney at a recent rally in Salt Lake City.

--CRUZ PUTTING UP A FIGHT IN UTAH: Texas Sen. Ted Cruz appears to be the favorite in the Beehive State, where 40 delegates are at stake for Republicans. He won the backing of Utah Gov. Gary Herbert on Monday. And former Republican presidential nominee Mitt Romney announced he would be voting for Sen. Ted Cruz. “At this stage, the only way we can reach an open convention is for Senator Cruz to be successful in as many of the remaining nominating elections as possible,” the former Massachusetts governor wrote on Facebook on Friday.

--IDAHO UP FOR GRABS: Democrats will get a chance to vote in Idaho, where 23 delegates are at stake on Tuesday. While it is an open caucus, Idahoans who voted in the Republican primary where Texas Sen. Ted Cruz nabbed a win, earning him 20 delegates, will not get a chance to participate. Hoping to win over Democrats of the Gem State, both Hillary Clinton and Bernie Sanders have paid the state their fair share of visits.

--ANALYSIS -- ABC’s RICK KLEIN: To know him is to love him or to hate him – and Republicans look likely to do some of both when it comes to Donald Trump, in the latest round of voting. Tuesday’s voting, in neighboring Arizona and Utah, appears likely to tell the GOP’s divide. Border-conscious and senior-heavy Arizona – home to Sheriff Joe Arpaio - seems poised to deliver all its delegates to Trump. Deeply religious and more pro-immigrant Utah – home to Mitt Romney – is likely to reject Trump overwhelmingly, with Ted Cruz in striking distance of turning the state into a winner-take-all. Trump is likely to walk away with the most delegates from the day, again. But the day figures to provide little to no clarity, beyond revealing the disparate faces of the GOP of 2016. No players will be able to declare clean victories, and the long, ugly slog of the nominating race will continue.

YESTERDAY ON THE TRAIL with ABC’s VERONICA STRACQUALURSI and PAOLA CHAVEZ

TRUMP REFERS TO SEN. ELIZABETH WARREN AS ‘THE INDIAN.’ Republican presidential candidate Donald Trump referred to Massachusetts Sen. Elizabeth Warren as “the Indian” at a news conference yesterday just hours after she unleashed a Twitter tirade against him. “Who is that, the Indian? You mean the Indian?” Trump asked, referring to Warren, who has said she has Native American ancestry. Warren’s contention became a point of controversy during her 2012 U.S. Senate race when her Republican opponent, former Massachusetts Sen. Scott Brown, who demanded proof. Warren has repeatedly defended her statements. ABC’s ALEXANDER MALLIN, PAOLA CHAVEZ and VERONICA STRACQUALURSI have more. http://abcn.ws/25g23Bv

CLINTON SLAMS TRUMP OVER ISRAEL-PALESTINE: ‘SOME THINGS AREN’T NEGOTIABLE’. Hillary Clinton used a speech yesterday on Israel and Palestine to slam her potential opponent in the general election, Donald Trump, accusing him of being unqualified to take on the challenges in the Middle East. “We need steady hands. Not a president who says he’s neutral on Monday, pro-Israel on Tuesday and who knows what on Wednesday because everything’s negotiable,” the Democratic presidential front-runner said during remarks at the American Israel Public Affairs Committee gathering in Washington, D.C., referring to Trump’s recent comment that he is “neutral” on Israel and Palestine. ABC’s LIZ KREUTZ and ALI DUKAKIS have more. http://abcn.ws/1pvA2VM

SANDERS CRITICIZES ISRAELI GOVERNMENT FOR TREATMENT OF PALESTINIANS. Bernie Sanders, the only Jewish presidential candidate this election cycle, was also the only candidate who elected not to attend the annual American Israel Public Affairs Committee (AIPAC) meeting this year. While all other candidates, including the remaining three Republicans and Hillary Clinton, spoke to the group in Washington, D.C., yesterday, Sanders instead took time while campaigning in Utah to deliver his own foreign policy speech, during which he had very pointed criticism for the Israeli government. During his remarks, which he described as the speech he would have given had he chosen to attend the powerful political lobby’s event yesterday, the senator called the U.S. and Israel long-term friends but said that because of that special relationship they were “obligated to speak the truth” to each other. ABC’s MARYALICE PARKS has more. http://abcn.ws/1pwkCRi

KASICH JABS TRUMP OVER ISRAELI-PALESTINIAN CONFLICT: ‘WE CANNOT BE NEUTRAL.’ Republican presidential hopeful John Kasich told the nation's most powerful pro-Israel lobbying group yesterday that the United States "cannot be neutral in defending our allies,” a clear jab at his rival Donald Trump, who recently said he would be “neutral" in dealing with the Israeli-Palestinian conflict. Kasich has over the past two weeks become more outspoken against Trump, who made the remarks about Israel last month, although he rushed through the line about neutrality yesterday to little applause. The Ohio governor also told attendees at the AIPAC conference in Washington that he believes the Iran nuclear deal should be suspended, ABC’s BEN GITTLESON reports. He had long said that it was unrealistic to think the deal could be torn up, as some of his rivals had called for, but two weeks ago said that Iran's recent ballistic missile tests should lead to the suspension of the deal. http://abcn.ws/1T4kUuB

ROMNEY RECORDS ROBOCALLS FOR TED CRUZ. Mitt Romney took his willingness to support Republican presidential candidate Ted Cruz one step further by recording robocalls for the Texas senator. In the calls, first reported by The Daily Caller, Romney encourages voters in Arizona and Utah to support Cruz. A call targeting Arizona voters was released yesterday and another call will begin ringing in Utah homes Tuesday. ABC’s JESSICA HOPPER notes, both Utah and Arizona will hold nominating contests Tuesday. “I’m calling to ask you to join me in supporting Ted Cruz for president this Tuesday in the Utah Republican caucuses. This is the time for Republicans across the spectrum to unite behind Ted,” Romney says in the call targeting Utah voters. "And at this point, a vote for John Kasich is a vote for Donald Trump.” http://abcn.ws/1o259Y7

IN CASE YOU MISSED IT

RAUL CASTRO DODGES QUESTION ABOUT WHETHER HE PREFERS TRUMP OR CLINTON. When Cuban leader Raúl Castro was asked which of two U.S. presidential candidates he preferred -- Hillary Clinton or Donald Trump -- Castro seemed to dodge the question, saying, "Well, I cannot vote in the United States," as the crowd laughed. President Barack Obama, who was standing alongside Castro, didn't comment, but seemed to enjoy the question, smiling in anticipation as he waited for Castro's answer. ABC’s EMILY SHAPIRO reports, Castro's lighthearted response came as he and Obama took questions from the press at a news conference in Havana. http://abcn.ws/25giBJV

WHO’S TWEETING?

@McCormickJohn: Trump's Republican Turnout Boost Extends to Battleground States http://bloom.bg/1RhliBg  via @bpolitics

@VaughnHillyard: Ted Cruz will hold a presser at 9:40 ET in DC to respond to the Brussels attacks.

@SenatorDurbin: Shocking reports of explosions a few hours ago at the Brussels airport and a metro station. America stands with Europe against terrorism.

@tripgabriel: Yesterday Trump suggested pulling back from NATO. Today, he says US is 'foolish' not to close borders.

‏@DavidMDrucker: Given certain Prez frontrunner's noninterventionism, might also be worthwhile to ask how his counter-terror strategy would differ from Obama