WASHINGTON (AP) — President Joe Biden's nomination of Neera Tanden to lead the White House Office of Management and Budget was thrown further into doubt on Monday as moderate Republican Sen. Susan Collins of Maine said she would vote against confirming Tanden.

On Friday, Sen. Joe Manchin of West Virginia became the first Democratic lawmaker to oppose Tanden's confirmation. But the White House called her "an accomplished policy expert who would be an excellent Budget Director,” and Biden said he was sticking with her.

Collins, though, said Monday that Tanden has “neither the experience nor the temperament to lead this critical agency,” which heads efforts to ensure an administration’s priorities are reflected in legislation and regulations. Collins blamed Tanden's past actions and said they “demonstrated exactly the kind of animosity that President Biden has pledged to transcend.”

During her confirmation hearings, Tanden apologized for spending years attacking top Republicans on social media. Tanden is a former adviser to Hillary Clinton and served as president of the liberal-leaning Center for American Progress. With the Senate evenly divided between 50 Republicans and 50 Democrats, and with Vice President Kamala Harris serving as a tiebreaking vote, losing Manchin means Tanden would need support from at least one Republican to win confirmation. Tanden really can’t afford to lose another Democratic vote.

The Senate Budget Committee is scheduled to vote on Tanden’s nomination this week. It’s the first real test that Biden has faced on a nomination, with most of his picks for Cabinet positions sailing through the chamber with bipartisan support.

Collins criticized Tanden for deleting tweets in the days before her nomination was announced and said that “raises concerns about her commitment to transparency.” She said Congress “has to be able to trust the OMB director to make countless decisions in an impartial manner, carrying out the letter of the law and congressional intent.”

“The OMB needs steady, experienced, responsive leadership," Collins said in a statement. "I will vote against confirming Ms. Tanden.”

Manchin said bipartisanship is “more important than ever” as the nation faces many crises and suggested Tanden was overtly partisan.

"I believe her overtly partisan statements will have a toxic and detrimental impact on the important working relationship between members of Congress and the next director of the Office of Management and Budget,” Manchin said in a statement.

Tanden had also disparaged some Democrats on social media, most notably Sen. Bernie Sanders, the independent from Vermont.

Biden, asked Friday whether he would pull Tanden’s nomination, said he wouldn’t.

“I think we are going to find the votes and get her confirmed,” Biden said.

Tanden, an Asian American, would be the first woman of color to lead the OMB. The White House said on Monday she has “lived experience having benefitted from a number of federal programs as a kid.”

"Looking ahead to the committee votes this week and continuing to work toward her confirmation,” White House press secretary Jen Psaki tweeted.