The victory -- winning at least 40 of Washington's delegates -- means Trump now has 1,229 of the 1,237 delegates he needs to clinch the GOP nomination, according to CNN estimates. Four more Washington delegates are still to be decided, potentially bumping Trump's total even higher.
Washington didn't have enough delegates to put him over the line Tuesday. Its results do, however, leave him inches short of it with a slate of contests on June 7 in California, New Jersey, New Mexico, Montana and South Dakota sure to seal the deal.
Trump became the presumptive nominee earlier this month with a decisive win in Indiana that forced his remaining rivals out of the race and ended months of talk about the potential of a contested convention.
News of Trump's victory was overshadowed on Tuesday night by the clashes between anti-Trump protesters and police outside his event in Albuquerque, New Mexico.
Protesters broke through police barricades, lit fires and threw rocks at the city's convention center, smashing one door. Some taunted police and jumped on police vehicles. Officers in riot gear and on police horses moved the protesters away from the convention center as anti-Trump chants rang through the city's streets.
Police in Albuquerque showed restraint, noting on Twitter late Tuesday evening that none of the protesters outside the Trump event had been arrested.
Trump is the last Republican standing in the presidential race -- but that didn't mean he was without opposition in Washington. The state's vote-by-mail contest featured ballots that included three other Republicans: Texas Sen. Ted Cruz, Ohio Gov. John Kasich and Ben Carson.
Cruz and Kasich quit the GOP race as ballots were being printed, and Carson never officially notified the state that he was dropping out.
As a result, the real contest in Washington is Trump vs. a not-Trump protest vote divided among those three candidates, all of whom have suspended their campaigns.
Meaningless vote for Dems
Washington also held a Democratic primary on Tuesday, but its results are meaningless.
It's one of the nation's most confusing procedures: Washington holds both primaries and caucuses for Democrats and Republicans.
Republicans chose to divvy up their delegates through the primary -- which is why Tuesday's contest mattered. But Democrats decided to allocate their delegates in the March 26 caucuses, where Vermont Sen. Bernie Sanders won all 39 counties and claimed the state by a 3-to-1 margin.
So Sanders will carry 74 delegates into the Democratic National Convention, while Hillary Clinton has 27 -- plus many of Washington's 17 superdelegates. That made Tuesday's primary results a popularity contest with no impact on the Democratic nomination.