Sen. Bernie Sanders plans to sign a party pledge affirming that he will run for president as a Democrat in 2020 and serve as one if elected, senior campaign adviser Jeff Weaver told CNN on Wednesday.

The Democratic National Committee said on Tuesday that it planned to meet in the coming week with the presidential primary campaigns and distribute a form to the candidates, who under bylaws agreed on last August will be required “to affirm in writing” that they “are a member of the Democratic Party, will accept the Democratic nomination” and “will run and serve as a member of the Democratic Party.”

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Sanders, an independent from Vermont who caucuses with Democrats in the Senate and ran in the party’s 2016 primary, announced his second White House bid on Tuesday morning. His refusal to more formally embrace the party has been a sore spot with some Democrats.

According to the DNC, all the announced campaigns have been invited to the meeting. Once they receive the form, they will have a week to return it.

“The DNC will present presidential campaigns that have currently announced their candidacy or the creation of an exploratory committee, with the rules and other materials next week at a briefing and this will include the candidate affirmation form,” a DNC official told CNN. “As any additional candidates enter the race, they will be provided with the same information and will be required to return the form in the same time frame.”

Despite the criticism from some in the party, Sanders entered the 2020 race with stronger Democratic support than he had four years ago. The rest of his state’s congressional delegation — Democrats Sen. Pat Leahy and Rep. Pete Welch — have endorsed him. In 2016, Leahy backed Hillary Clinton and Welch withheld his support for Sanders until just before the Vermont primary.

Sanders declined the Democratic nomination in all three of his Senate campaigns, choosing to run as an independent after winning the party’s primary.

In 2016, he declared as a Democrat in New Hampshire to participate in the presidential primary there, as required by the state’s rules. The move was challenged by a local Republican, but Sanders was ultimately permitted to run by the state’s ballot commission since Vermont does not have party registration. New Hampshire Democratic Party Chairman Ray Buckley defended Sanders’ placement on the party’s ballot.