WASHINGTON – Sen. Bernie Sanders signed a pledge, required under new Democratic National Committee rules, that declared he was a Democrat and would serve as one if elected president, according to media reports.

Sanders, an independent from Vermont, is one of more than a dozen candidates who has launched a presidential bid or announced an exploratory committee for a White House run. He signed the pledge, which was given to all 2020 candidates for their signature, on Tuesday, according to a copy obtained by NBC News.

"I am a member of the Democratic Party," the document signed by Sanders reads. "I will run a Democrat, accept the nomination of my Party, and I will serve as a Democrat if elected."

The document also states that the DNC has the authority to determine whether a candidate is indeed a "bona fide Democrat," saying the committee would examine the candidate's record, writings and accomplishments.

The new DNC rule is part of a number of changes within the organization.

It was partially enacted as a response to Sanders' 2016 presidential campaign, which he lost to Hillary Clinton. Sanders ran as a Democrat but was a longtime independent and self-described democratic socialist. Some Democrats had worried during the primary fight that Sanders could run as an independent if he lost to Clinton, something Sanders did not do.

There was also question over whether Sanders should qualify for the primaries since he was registered as a Democrat.

Sanders caucuses with Democrats but has consistently run for office as an independent, including on Monday when Sanders filed to run again for his Senate seat in 2024, according to NBC News.

Since the 2016 race, the DNC has also scaled back the role of superdelegates in presidential nominations, which Sanders and his supporters rallied for.

The change came after complaints about party insiders' incredible influence in the primary process. Superdelegates announcing support for Clinton gave her an early advantage in the primary, and their role was a major point of contention for Sanders’ supporters.