Hillary Rodham Clinton is in the most commanding position by far in the Democratic race.
Vermont Senator Bernie Sanders, a self-described democratic socialist, stepped up in April to take her on and court the party's left.
So what does Martin O'Malley, who entered the contest Saturday, have to offer liberals that Sanders doesn't?
Achievement, he told ABC's "This Week."
"I have a track record of actually getting things done, not just talking about things," O'Malley said when asked to compare himself with Sanders, an independent in the Senate who aligns with Democrats. O'Malley served as Maryland governor and Baltimore mayor.