Joe Biden has been declared the winner —narrowly — of last week's Democratic presidential primary in Washington state, giving him victories in five out of six states that voted March 10. According to the Washington secretary of state's website, Biden won 37.8% of the vote, compared to Bernie Sanders' 36.4%.

After nearly a week of counting votes, the former vice president on Monday held onto a small lead over Sanders that turned out to be insurmountable.

Washington was a state that Sanders had been hoping to win. In 2016, he won more than two-thirds of the delegates from the Washington caucuses over Hillary Clinton.

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Of the state's 89 pledged delegates, only 31 are allocated based on the statewide result. The remaining 58 are determined based on the results of the state's 10 congressional districts, and those results might not be calculated until the election is certified by the secretary of state's office, which could be as late as March 27.

Biden won four other states last Tuesday: Missouri, Mississippi, Michigan and Idaho. Sanders won North Dakota.

In Washington, Democrats used the vote-by-mail presidential primary — moved up this year from May — for the first time to allocate delegates instead of the smaller caucuses used in previous years.

Four states — Arizona, Ohio, Illinois and Florida — are scheduled to hold primaries on Tuesday. Biden, during a virtual town hall event, was asked Monday evening about how to vote safely Tuesday, in light of the threat of the coronavirus.

He advised her to remain six feet away from other voters in line and advised her that the voting machine would be wiped down and she would also receive a wipe for her hands after voting. Listen to the health experts, he counseled.

Bo Erickson contributed to this report.