Martin O'Malley doubled down on his frequent campaign theme of being the only "lifelong Democrat" in the race Friday.

"I think that when President Obama was running for re-election, I was glad to step up and work very hard for him," the former Maryland governor said to Rachel Maddow at Friday's MSNBC Democratic forum.

"Senator Sanders was trying to find someone to primary him," O'Malley said regarding his rival Bernie Sanders. "I am Democrat. I am a lifelong Democrat."

Sanders was receptive to the idea of finding a primary challenger to Obama in the last election.

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