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The manager of former Gov. Martin O’Malley’s presidential campaign is urging other Democratic campaign managers to agree to five additional debates in the early states.

Dave Hamrick, who is managing Mr. O’Malley’s campaign, sent a letter to the campaign managers on Sunday, asking that they also press the Democratic National Committee to drop its clause sanctioning the debates.

“By limiting the number of debates Democrats hold this year, the D.N.C. is allowing the Republican presidential candidates — namely, Donald Trump — to dominate the national debate, and whoever our nominee is will emerge stronger as the result of a vigorous debate process,” Mr. Hamrick wrote.

“Specifically, we are asking for two additional weeknight, nonholiday peak season debates in Iowa and New Hampshire respectively, and one additional weeknight, nonholiday peak season debate in South Carolina and Nevada, respectively,” he said, asking for those to fall before Feb. 1, 2016.

In the letter, he noted that two of the party committee’s vice chairmans have called for an increase in debates, taking issue with the current process. But the party committee has said it will not budge.

Mr. O’Malley, the former Maryland governor whose poll numbers have remained low, has been leading the call for more debates, with a singular focus.

A spokeswoman for Hillary Rodham Clinton declined to comment. A spokesman for Senator Bernie Sanders said that the candidate had already called for more debates.