Bernie Sanders is the projected winner of the Idaho Democratic caucuses, according to CNN.
Ted Cruz is the projected winner of the Utah GOP caucus, according to NBC. NBC also projected Bernie Sanders as the winner of the Utah Democratic caucuses.
Sanders' win comes after Hillary Clinton was named the projected winner of the Arizona Democratic primary late Tuesday night.
Donald Trump won the Arizona GOP primary, according to projections.
Ted Cruz hopes to slow Trump's march toward the Republican nomination while Democrat Bernie Sanders is seeking a bounce-back win in Tuesday's Western nominating showdowns overshadowed by a day of terror in Brussels.
Both parties are holding primaries in Arizona and caucuses in Utah, while Democrats also have caucuses in Idaho. The trio of races come with front-runner Trump and Clinton established as strong favorites for their parties.
Republicans have a total of 98 delegates at stake while Democrats are competing for 131 delegates.
In Utah, Texas Sen. Cruz is eyeing a 50% winner-take-all threshold that would allow him to harvest all 40 delegates. If he falls short, the delegates will be doled out in proportion to each candidate's vote share.
Cruz goes into the caucuses after securing the endorsement of Mitt Romney in a state with a high concentration of the former Republican nominee's fellow Mormons.
Romney told Republicans in a robocall that a vote for Cruz's rival, Ohio Gov. John Kasich, was effectively a vote that would make it easier for Trump to win the 1,237 delegates needed to win the nomination.
Cruz still has a mathematical path to the nomination but his main hope lies in stopping Trump short of that magic number and prevailing in a contested Republican National Convention in Cleveland in July. The same applies to Kasich.
Trump, meanwhile, is seeking a big win in Arizona, a state where his vow to deport undocumented migrants and plans for a border wall are expected to resonate with Republican voters.
Tuesday's primaries will not change the dynamic in the Democratic presidential race in which Clinton has a wide lead.
Although polling is sparse in the states being contested Tuesday, Sanders is hoping for morale-boosting wins after drawing a blank in five big contests throughout the Midwest and the South last week that helped Clinton pad her lead in delegates.
In Idaho, a huge turnout is expected and the state capital of Boise could see the largest single caucus in history, with 10,000 to 12,000 Democrats expected to cast ballots, according to organizers.
The candidates' regular election-day get-out-the-vote efforts were replaced by an escalating political battle over ISIS-claimed terror attacks in Belgium. Candidates conducted a flurry of television interviews staking out ground on national security to bolster their credentials as potential presidents.
The Cruz campaign said the attacks in Brussels could give its candidate an opening to distinguish himself from other candidates, including Trump.
"This is Major League vs. T-ball," a Cruz campaign official said.
According to the latest CNN delegate estimate, Clinton now has 1,656 delegates, including 1,174 pledged delegates and 482 superdelegates. Sanders has 877 delegates, including 850 pledged delegates and 27 superdelegates.
A total of 2,383 delegates is needed to clinch the nomination.
On the Republican side, Trump leads with 683 delegates. Cruz has 421 and Kasich has 145.