After the Democratic National Committee announced in May that it would sanction just six presidential primary debates, Sen. Bernie Sanders (I-Vt.) objected.

He wrote DNC Chairwoman Debbie Wasserman Schultz a letter calling for a "a series of debates beginning this summer." He urged supporters to sign a petition requesting the same. And he told Chuck Todd, moderator of NBC's "Meet the Press," that he'd like to debate Republican presidential candidates, too.

Those pleas, apparently, fell on deaf ears. 

On Thursday, the DNC unveiled its debate schedule — and it still plans to allow just six. In a written statement, Sanders said he was "disappointed, but not surprised" by the news.

"At a time when many Americans are demoralized about politics and have given up on the political process, I think it's imperative that we have as many debates as possible — certainly more than six," he said. "I look forward to working with the DNC to see if we can significantly expand the proposed debate schedule."

Four of the DNC's debates will take place before the all-important Iowa caucuses and New Hampshire primary. Candidates will meet in Nevada on October 13; in Iowa on November 14; in New Hampshire on December 19; and in South Carolina on January 17. Later in the primary season, in February or March, they'll meet in Florida and Wisconsin.

Thursday's announcement was widely greeted as good news for Democratic frontrunner Hillary Clinton, who will have fewer chances to stumble on her way to the winter nominating contests. It was seen as bad news for Sanders and other candidates seeking to share the stage with her. Former Maryland governor Martin O'Malley, who has trailed both Clinton and Sanders, appeared most upset with the decision, accusing the DNC of making the process "less democratic."

"If anything, it seems geared toward limiting debate and facilitating a coronation, not promoting a robust debate and primary process," O'Malley said in a statement.