Sen. Bernie Sanders (I-VT) will reportedly pledge to run for president in 2020 as a Democrat and serve as a Democrat if elected.

Jeff Weaver, Sanders’ senior campaign adviser, reportedly told CNN on Wednesday evening that Sanders plans to sign the pledge that the Democratic National Committee (DNC) is requiring presidential candidates to sign.

Candidates running in the party’s primary will be reportedly 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.”

“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 reportedly 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.”

CNN points out that “Sanders declined the Democratic nomination in all three of his Senate campaigns, choosing to run as an independent after winning the party’s primary,” and “his refusal to more formally embrace the party has been a sore spot with some Democrats.”

Rep. Gregory Meeks (D-NY) on Thursday said that the difference between former Vice President and potential presidential candidate Joe Biden and Sanders is that “Bernie Sanders is not a Democrat.”

“We’ve asked him on a continuous basis if, in fact, you want to be the Democratic nominee, you should be a Democrat,” Meeks said of Sanders. “If you’re not a Democrat, you should not run. He should run as an independent. He’s not a Democrat. So, to me, I wouldn’t allow a Republican to run as a Democrat. … If he wants to be a Democrat, he should register to be in the Democratic Party.”