The Democratic National Committee is looking ahead to unseating President Trump in 2020 but their latest rule change may actually narrow the field of contenders.

A new rule, adopted at a DNC meeting in Providence, R.I. on Friday, requires all candidates for the party’s nomination to “run and serve” as Democrats, Yahoo News reported.

While Sanders supporters could condemn the showboating by Democrats as getting back at the Vermont senator for his strong run against Hillary Clinton in the 2016 primaries, a source told Yahoo that it was actually more of an effort to limit the power of so-called superdelegates.

Superdelegates from states Sanders won chose not to vote for the self-described democratic socialist at the party’s 2016 convention in Philadelphia, thereby ensuring Clinton clinched the party’s nomination.

Randi Weingarten, DNC member and president of the American Federation of Teachers, posted a photo of the rules change from the meeting in Providence.

@DNC #RBC just changed the rules to ensure to run for President as a Democrat you need to be A Democrat pic.twitter.com/RyHhV0Exhr — Randi Weingarten (@rweingarten) June 8, 2018

“At the time a presidential candidate announces their candidacy publicly, they must publicly affirm that they are a Democrat,” the new rule states. “Each candidate pursuing the Democratic nomination shall affirm, in writing, to the National Chairperson of the Democratic National Committee that they: A. are a member of the Democratic Party; B. will accept the Democratic nomination; and C. will run and serve as a member of the Democratic Party.”

According to Yahoo News:

With Sanders’s independent status and push for inclusivity, the new rule change would seem to be a slap in the face and a potential roadblock should the Vermont senator decide to mount another presidential run in 2020. However, Sanders allies do not believe he would be affected by the measure thanks to a unique rule in his home state. Sanders, who is currently running for reelection, typically runs in the state’s Democratic primary but declines the party’s nomination after winning. The move allows him to fend off Democratic challengers in the state while still running as an independent. Last month, the Vermont Democratic Party passed a resolution supporting this strategy and proclaiming that Sanders would still be considered a member of the party “for all purposes and entitled to all the rights and privileges that come with such membership at the state and federal level.” That membership could inoculate him against the DNC’s rules change.

Mark Longabaugh, a senior adviser to Sanders’s 2016 presidential campaign, was perplexed by the party’s new rule change.

“I don’t have any worries that Bernie Sanders could meet the criteria to run as a Democrat in 2020, but it always puzzles me that there are some Democrats who want to do this and promote this. I scratch my head and ask why they would want to make the party more narrow and more exclusive,” Longabaugh told Yahoo.

“We just came off a devastating presidential loss in 2016. It would seem to me the actual impetus would be to expand the Democratic Party. I just for the life of me don’t see any motivation for this beyond personal spite,” he said.

The contention that the rule is aimed at eliminating Sanders from the process was refuted by one source who told Yahoo that the goal would ultimately achieve one of Sanders’s main priorities — the end of superdelegates, though it seems a bit of a stretch to see a correlation between that aim and a new rule requiring a kind of party loyalty pledge.

“With the full DNC heading toward the path of essentially eliminating superdelegates on the first ballot, people felt this would help garner support for the superdelegate proposal,” the source said.

Sanders’s former campaign manager, however, sees the rule change as a means to exclude some people from the presidential nominating process of the Democratic Party.

“Do they really want Bernie and millions outside the party?” Jeff Weaver asked.

DNC members plan to meet in August for a final vote on the proposal to eliminate superdelegates.