The Vermont senator tried to build his enduring support among liberal activists into a three-state sweep that could help him narrow the gap with Clinton.
The former secretary of state had won 300 more delegates than Sanders in state primaries and caucuses before yesterday's contests. The two Democrats were also competing in Hawaii's caucuses.
While Sanders faces a steep climb to the nomination, a string of losses for Clinton would highlight persistent vulnerabilities within her own party.
Speaking at a campaign rally in Madison, Wisconsin, before voters in Hawaii gathered for their caucuses, Sanders cast his wins yesterday as part of a Western comeback, citing recent victories in Utah and Idaho as a sign that his campaign still had a path to the nomination.
"We just won the state of Washington. That is what momentum is about," he said. "Don't let anybody tell you we can't win the nomination or we can't win the general election. We're going to do both of those things."