Neera Tanden, president of the Center for American Progress and a former Hillary Clinton aide, blamed Clinton’s poor polling on her primary opponent, Sen. Bernie Sanders (I., Vt.), during an interview posted Monday. While many polls show Clinton beating Donald Trump, polls also show most people having a negative view of the Democratic nominee.

Tandem placed the blame on Sanders’ attacks against Clinton during their primary battle in an interview with Politico’s Glenn Thrush, adding that the Vermont senator has let Trump continue those attacks in the general election.

"He did do significant damage to Hillary’s negatives," Tanden said. "I mean, he drove a lot of those negatives, and the truth of it, I mean, just to be candid or honest about it, you know, I think getting those kinds of attacks from another Democrat or another liberal or another progressive is much tougher for Hillary, and it was really hard."

"If you look at her trust numbers the last six months of that primary, it was much, those numbers took a much sharper dive and hard to recover from," Tanden said.

Sanders had attacked Clinton during the Democratic primary by calling her out on her connections with Wall Street firms and for being part of the Democratic establishment. Sanders, however, did not criticize her for her use of a private email server while she was secretary of state.