Neera Tanden, Joe Biden's nominee to head the Office of Management and Budget, previously criticised Democratic Senator Joe Manchin's daughter, a slight that might factor into whether or not she is confirmed for the position.
Ms Tanden tweeted an image of an article about Mr Manchin's daughter, Heather Bresch, taking aim at a significant increase in her pay while she was CEO of Mylan.
In the tweet, Ms Tanden pointed out that the company's board was justifying the pay raise by saying Ms Bresch had "contributed significantly to the company's growth in recent years".
Ms Tanden said that the "idea that only CEO contributes to a company's growth and not all employees is really pernicious".
Ms Tanden was a prolific Twitter user prior to her nomination for the OMB, often getting into squabbles with both conservatives and progressives. Her Twitter feuds occurred with lawmakers, journalists, and general users.
The Democratic operative deleted 1,000 tweets ahead of her confirmation hearing.
Her Twitter behaviour has become a major sticking point in her nomination hearing, with several Republicans vowing they would never support her for the position. Mr Manchin also said he would oppose her nomination, citing her comments towards lawmakers.
"I have carefully reviewed Neera Tanden's public statements and tweets that were personally directed towards my colleagues on both sides of the aisle from Senator [Bernie] Sanders to Senator [Mitch] McConnell and others," Mr Manchin said in a statement. "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."
He said that supporting her nomination would be inappropriate considering the toxic political climate in the US.
"For this reason, I cannot support her nomination. As I have said before, we must take meaningful steps to end the political division and dysfunction that pervades our politics. At a time of grave crisis, it is more important than ever that we chart a new bipartisan course that helps address the many serious challenges facing our nation," he said.
Among Ms Tanden's tweets were attacks on progressives, including Sen. Bernie Sanders, which he addressed during her confirmation hearing.
“There were vicious attacks made against progressives, people who I have worked with, me personally,” Mr Sanders said.
A progressive student group, RootsAction, spoke with The New York Times about Ms Tanden, and said she is considered an extreme opponent to progressive ideas.
“Tanden has become known as one of the most prominent anti-progressive voices of the neoliberal establishment,” the group said.
Ms Tanden has apologised multiple times for her tweets.
Ms Tanden was named to Hillary Clinton's transition team after she clinched the 2016 Democratic presidential nomination, and was considered very likely to have been given a permanent position in Ms Clinton's administration.
The White House has continually defended Ms Tanden's selection to run the OMB. White House Press Secretary Jen Psaki has made multiple statements backing the nominee despite the Senate's concerns.
"Neera Tanden is a leading policy expert who brings critical qualifications to the table during this time of unprecedented crisis. She also has important perspective and values, understanding firsthand the powerful difference policy can make in the lives of those going through hard times," she tweeted. "She has a broad spectrum of support, ranging from the U.S. Chamber of Commerce to labor unions, and has a strong record of working with both parties that we expect to grow in President Biden's cabinet as the first South Asian woman to lead OMB."
Ms Tanden’s confirmation hearing has been postponed to allow members more time to consider her nomination.