OLYMPIA, Wash. (AP) — Early returns in vote-by-mail Washington show a tight race between Vermont Sen. Bernie Sanders and former Vice President Joe Biden.

With the state's 39 counties posting their first batch of results Tuesday, Sanders led by about 2,000 votes, but it will take days to receive and tally all the votes. Counties will update their results again Wednesday afternoon.

More than 1.5 million votes of the more than 1.8 million received to date were counted Tuesday night. Results could continue to change as ballots dropped in drop boxes Tuesday or those which may still be in the mail arrive at elections offices and are processed.

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.

Democrats are using 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.

The Washington ballot had 13 candidates on it, along with an ‘uncommitted’ option. But it was essentially a two-person race between former Vice President Joe Biden and Vermont Sen. Bernie Sanders. President Donald Trump was the only candidate listed for Republicans. Trump received more than 523,000 votes, and more than 8,000 Republican wrote in an alternate candidate. More than 356,000 Democrats voted for candidates other than Biden or Sanders.

In 2016, Sanders won more than two-thirds of the delegates from the Washington caucuses that year, which were attended by about 230,000 Democrats. More than 800,000 Democrats sent in ballots for the primary later that year — which Hillary Clinton won — even though their vote didn't count for the nominating process.

The state Democratic Party's central committee voted last year to start using a hybrid system that uses the state’s vote-by-mail system for a presidential primary to apportion delegates to candidates, and caucuses and conventions to select which delegates will represent the state at the national convention in Milwaukee in July. Also last year, Washington Gov. Jay Inslee signed a measure moving the state's presidential primary from May to the second Tuesday in March.

Both parties have rules that only voters who identify with a party may participate in the primary to allocate delegates to the national nominating conventions. Washington state has no party registration, and in order to have their vote in the presidential primary counted, voters must sign a pledge on the envelope affirming to being either Republican or Democrat. They can only vote in the race that corresponds with their party. As of Tuesday night, more than 65,000 ballots were at risk of being invalidated because a party was not chosen, or in the case of 781 voters, they chose both parties. Elections officials will contact each of those voters to see if they want to select a party in order to have their vote count.

Will Casey, a spokesman for the state Democrats, said that under Democratic National Committee Rules, if any listed candidate hits the 15 percent threshold in voting, they are allotted delegates, even if no longer in the race. Those delegates will be pledged to that candidate on the first ballot, though they can ultimately be released by that candidate. As of Tuesday night, no one other than Biden and Sanders surpassed the 15 percent threshold.