One of the largest advocacy groups to endorse Bernie Sanders on Wednesday gently nudged the Vermont senator toward the exit, arguing that the Democratic nomination can’t be won on the backs of “undemocratic superdelegates.”

The liberal group MoveOn.org suggested in a statement that Hillary Clinton fairly earned the Democratic nomination after Tuesday’s primaries by clinching a majority of pledged delegates.

“MoveOn members believe, as we have long advocated, that the nomination should go to the winner of the majority of pledged delegates, and that undemocratic superdelegates should not overturn the will of the voters,” MoveOn Political Action’s Executive Director, Ilya Sheyman, said in the statement.

Sanders won MoveOn’s endorsement in January with over 78 percent of the 340,665 votes cast by the group’s members.

In the statement, Sheyman applauded Sanders for revolutionizing “politics as we know it” with his grassroots campaign and insisted that “the policies Bernie has advanced should be included in the Democratic platform.”

Sheyman said that Sanders “has more than earned the right to figure out the next steps for this movement on his own timeline,” but he implied that Clinton’s status as the presumptive nominee after landslide primary wins in New Jersey and California, which secured her lead in both pledged delegates and super-delegates, shut the door on Sander’s hopes for a contested convention. The former secretary of state also leads Sanders in the popular vote.

Sanders renewed his vow to remain in the race until the Democratic National Convention in July after Tuesday’s primaries, and his campaign has said it believes it can persuade some superdelegates to flip their support from Clinton to him.

But even some of the Vermont senator’s most prominent backers have rejected that strategy.

As Sanders’ sole endorser in the Senate, Jeff Merkley of Oregon, said, “We have our nominee.”