Updated

President Biden is standing behind a pair of Cabinet picks facing uphill battles -- including Neera Tanden, his nominee to lead the Office of Management and Budget, and Xavier Becerra, his pick for secretary of the Department of Health and Human Services -- as a growing number of senators have vowed to oppose their confirmations.

Tanden's confirmation appears to be the most in jeopardy after several swing vote senators -- including at least one Democrat -- have announced plans to vote against her confirmation. The former president of the liberal Center for American Progress repeatedly came under fire during her confirmation hearing, as Republicans pointed to hostile tweets she posted against various lawmakers -- many of which she deleted late last year.

CONSERVATIVES CALL BIDEN PICK FOR HHS XAVIER BECERRA AN 'EXTREMIST,' OPPOSE NOMINATION

During that hearing, Sen. Ron Portman, R-Ohio, gave examples of "a few of the thousands of negative public statements" Tanden has made. These included her calling Sen. Susan Collins, R-Maine, "the worst" and Sen. Tom Cotton, R-Ark., a "fraud," saying that "vampires have more heart than Ted Cruz," and referring to then-Senate Majority Leader Mitch McConnell, R-Ky., as "Moscow Mitch" and "Voldemort," referring to the Harry Potter villain.

Portman said that even after Tanden deleted tweets, there were still nine pages of posts about Cruz that were still up.

"I wonder, specifically, how do you plan to mend fences and build relationships with members of Congress you have attacked through your public statements?" Portman asked.

President Biden is standing by Xavier Becerra, Neera Tanden amid uphill confirmation battles (Getty images)

"I recognize the concern," Tanden replied. "I deeply regret and apologize for my language — some of my past language. I recognize that this role is a bipartisan role, and I know I have to earn the trust of senators across the board. I will work very aggressively to meet that concern."

COLLINS OPPOSES TANDEN FOR BIDEN BUDGET DIRECTOR, IN ANOTHER BLOW TO CONFIRMATION

Tanden said she hopes to work "in a bipartisan and nonpartisan manner," while acknowledging that "it’s upon me to prove that to this committee and to members."

But following the hearing, Democratic Sen. Joe Manchin, D-W.V., said he would oppose her nomination, citing her tweets, and saying that 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."

"For this reason, I cannot support her nomination," Manchin said.

Manchin's opposition meant Tanden will need Republican support. But that effort to woo a Republican was hampered when Collins also said Monday she would vote against Tanden—dealing another blow to her confirmation.

"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," Collins said in a statement on Monday. "Neera Tanden has neither the experience nor the temperament to lead this critical agency."

But the White House is still standing behind her, vowing not to pull her nomination, even though it's unclear how Tanden will cobble together enough votes.

"The president nominated her because he thought she would be stellar," White House press secretary Jen Psaki said Monday, noting her experience.

When asked if they still felt her confirmation was possible, Psaki said: "We do."

Meanwhile, another Biden pick is facing heightened scrutiny, with Becerra getting ready for his confirmation hearing in the Senate on Tuesday as Republicans have signaled plans to focus on trying to torpedo his nomination. But he could also have problems with Democrats: Manchin's office says he hasn't decided whether he'll support Becerra.

More than 100 conservatives sent a memo to Republican members of Congress outlining their concerns with Becerra’s nomination, calling him an "extremist" who would carry a liberal agenda if confirmed.

MANCHIN TO OPPOSE BIDEN OMB PICK NEERA TANDEN OVER CONTROVERSIAL TWITTER POSTS

"Becerra has shown neither the judgment, character, or respect for human life necessary to lead the agency with such influence over the foundational rights of all Americans," they continued. "Under his watch, we believe HHS – an agency that should protect human life, dignity, and enshrine the values of religious liberty – would be weaponized toward partisan and destructive ends."

They added: "For all these reasons, we urge the Senate to firmly reject his confirmation."

Conservative groups have also taken issue with Becerra leading HHS amid the coronavirus pandemic, saying he has "no health care experience," and instead, that a doctor or public health care expert should be leading the department.

Biden transition spokesman Andrew Bates defended Becerra, saying he has "decades of health care policy experience, worked with Republicans and Democrats to expand access to COVID treatments and take on opioid manufacturers, while leading the largest state department of justice in the country."

Bates added that Becerra also has a "strong record of fighting to lower costs for patients."

BIDEN OMB PICK TANDEN CALLED OUT DURING CONFIRMATION HEARING FOR ANTI-GOP TWEETS, SAYS 'I'M SORRY'

"That's why President Biden chose this tested, qualified leader to be at the forefront of the pandemic response and to help lower drug prices," Bates said. "We look forward to his hearings and confirmation votes." 

And Psaki on Monday, during her briefing, said Becerra "helped play a role in getting the Affordable Care Act through" and "brings decades of health care policy experience to the table." 

Psaki pointed to Becerra's work as California attorney general, saying he "fought alongside his Republican counterparts to expand access to COVID treatments." 

Despite conservative opposition, the Biden transition team told Fox News that Becerra is looking forward to "working in good faith with members of both parties in Congress."

Meanwhile, Biden’s pick for attorney general Judge Merrick Garland also appeared this week for his confirmation hearings before the Senate Judiciary Committee. Garland was pressed on hot-button issues but lawmakers on the committee, including Republicans, indicated he would likely be confirmed.

Fox News’ Megan Henney, Brittany De Lea, and Paul Steinhauser contributed to this report.