(CNN) 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."

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.

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