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Vermont Sen. Bernie Sanders clarified his support for Jon Ossoff on Friday, after catching flack for saying earlier that he didn’t know if the Democratic congressional candidate is a progressive.

“Let me be very clear. It is imperative that Jon Ossoff be elected congressman from Georgia's 6th District and that Democrats take back the U.S. House,” Sanders said in statement. “I applaud the energy and grassroots activism in Jon's campaign. His victory would be an important step forward in fighting back against Trump's reactionary agenda.”

It was an attempt to clean up an earlier comment Sanders made, which led to accusations that he was undermining both Ossoff, in whom many Democrats have invested their hopes, and an ongoing tour with Democratic National Committee Chair Tom Perez that was intended to demonstrate the party’s unity.

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In interview with the Wall Street Journal Wednesday, Sanders answered “I don’t know” when asked if Ossoff is progressive. “Some Democrats are progressive, and some Democrats are not,” Sanders said .

Even some of Sanders’ ideological allies objected to the comment. David Nir, the political director of the liberal blog Daily Kos, which has raised millions for Ossoff, said on Twitter that Sanders was “hurting“ the cause.

Bernie Sanders isn't helping—he's hurting. He should either endorse Ossoff and raise money for him, or keep his silence https://t.co/G6YzNTRWHB — David Nir (@DavidNir) April 19, 2017

The tensions were further elevated by the fact that Sanders praised a mayoral candidate in Omaha, Nebraska, who was revealed to have a mixed record on abortion.

At Sanders' request, the DNC added a stop on the tour to promote Health Mello, prompting backlash from pro-choice groups and accusations that Sanders was applying a double standard — or perhaps a loyalty test — about what it means to be a progressive.

Perez, who skipped the Omaha stop in order to campaign for Ossoff, had to put out his own clarifying statement Friday.

"I fundamentally disagree with Heath Mello’s personal beliefs about women’s reproductive health. It is a promising step that Mello now shares the Democratic Party’s position on women’s fundamental rights. Every candidate who runs as a Democrat should do the same, because every woman should be able to make her own health choices. Period,” Perez said.

Ossoff narrowly fell short of winning a special congressional election in Georgia this week, pushing him into a runoff election in June against Republican Karen Handel.