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Five people who served on President Obama’s national finance committee during his first presidential campaign are circulating a letter seeking to rally support for Martin O’Malley, the former governor of Maryland who has been struggling to gain traction in the Democratic presidential race.

The five Obama supporters — Mark Alderman, Dan Hynes, Dixon Slingerland, Ed Redlich and Sarah Timberman — suggested in the letter that they believe Mr. O’Malley “can and should win” against Hillary Rodham Clinton and Senator Bernie Sanders of Vermont.

They described Mr. O’Malley as a “true progressive” who represents a “new generation of leadership.”

Mr. O’Malley’s aides have trumpeted his consistent support of Mr. Obama’s record, noting that he was one of the few Democrats to travel the country in support of the president’s re-election in 2012 as a surrogate. That support has drawn renewed focus as Mr. Sanders has increasingly suggested that he backs Mr. Obama’s record.

“We know that a lot of you have already supported Secretary Clinton, and a good number of you had been waiting on the sidelines until the vice president made his ultimate decision,” the supporters wrote of Vice President Joseph R. Biden Jr.’s recent flirtation with joining the race. “We are urging you to give Martin a very serious look.”

They added, “We, of all people, should not be afraid to take a chance on someone who is down in the polls.”

Mr. O’Malley has remained in the low single digits in national and state polls, despite aggressively campaigning for the last year.