Longtime Hillary Clinton Hillary Diane Rodham ClintonBiden leads Trump by 36 points nationally among Latinos: poll Democratic super PAC to hit Trump in battleground states over coronavirus deaths Battle lines drawn on precedent in Supreme Court fight MORE confidante Neera Tanden in a new podcast commends Bernie Sanders Bernie SandersNYT editorial board remembers Ginsburg: She 'will forever have two legacies' Two GOP governors urge Republicans to hold off on Supreme Court nominee Sanders knocks McConnell: He's going against Ginsburg's 'dying wishes' MORE for the issues he raised during his campaign but notes his attacks on the Democratic presidential nominee were harmful.

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“I actually have to say, I think he brought a lot of really important issues to the floor, but Senator Sanders was prosecuting a much tougher character attack” than Barack Obama Barack Hussein ObamaDemocratic Senate campaign arm outraises GOP by M in August A federal court may have declared immigration arrests unconstitutional Blunt says vote on Trump court nominee different than 2016 because White House, Senate in 'political agreement' MORE did in 2008, Tanden said during Politico’s “Off Message” podcast.

“He did do significant damage to Hillary's negatives."

During the primary season, the Vermont senator often attacked the eventual Democratic nominee on the campaign trail — at points, questioning her judgment.

“I mean, he drove a lot of those negatives, and the truth of it, I mean, just to be candid — or honest about it, I think getting those kinds of attacks from another Democrat or another liberal or another progressive is much tougher for Hillary," said Tanden, who is the president of the liberal think tank Center for American Progress.

"If you look at her trust numbers the last six months of that primary ... those numbers took a much sharper dive and [were] hard to recover from.”

Sanders endorsed Clinton ahead of the Democratic National Convention, vowing to help the Democratic nominee win the presidency.

But Tanden, who supported Clinton's shift to the left due in part to Sanders's criticism, said the Vermont senator may have let the primary stretch out too long.

"The primary was much tougher [than 2008]," she said.

"There were many more open attacks on being 'bought and paid for' and all that stuff."