Mayor Bill de Blasio, on a grassroots campaigning mission for Hillary Clinton in Iowa, defended his former boss against criticism that she was slow to embrace the fight against income inequality, an issue on which de Blasio has staked his mayoralty.

Vice President Joe Biden told CNN in mid-January said “it’s relatively new for Hillary to talk about that” while her main rival for the Democratic presidential nomination, Bernie Sanders, has “credibility” and “authenticity” on addressing the gap between rich and poor.

De Blasio said on MSNBC Sunday that he’s “surprised at Biden, honestly.”

“I never questioned that she had a rich, progressive tradition, and I’m surprised he didn’t remember what she did on health care reform in 1993 and 1994,” the Democratic mayor said of Clinton’s campaign for universal health care as first lady.

But de Blasio himself had delayed his endorsement of the former secretary of state for six months, citing a need to hear more from her on income inequality. The mayor finally gave Clinton his formal nod in October. He served as campaign manager of her successful 2000 U.S. Senate race.

The mayor on Sunday commended Sanders, the U.S. senator from Vermont challenging Clinton, for campaigning about the need to boost the working class through paid leave, higher minimum wages and other means “so eloquently, so powerfully.”

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De Blasio said his candidate, however, can get things accomplished. “That’s where the discussion tips very favorably to Hillary because of a whole history of actually knowing how to get something done for a progressive cause,” he said.

The mayor and New York City first lady Chirlane McCray are in the midst of a five-day campaigning trip for Clinton in Iowa, which holds its caucuses on Monday. De Blasio is not expected to cross paths with Clinton.

De Blasio has encountered voters who don’t know him, he told MSNBC “PoliticsNation” host the Rev. Al Sharpton.

Some of them know the work I’ve done, some don’t, but the most important thing is to have those people-to-people conversations,” he said.

De Blasio told 77 WABC Radio that he is “knocking on doors, phone banking, talking to local activists, whatever it takes to help turn out folks for caucus night.”

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He acknowledged he won’t likely have a starring role at rallies for Clinton.

“I don’t think of it as high-profile. I think of it as doing the same kind of thing I’ve done in previous cycles: to go and turn out the vote,” de Blasio said.