WASHINGTON (AP) — The White House is standing by President Joe Biden's choice of Neera Tanden to lead the White House budget office, even as she faced new hurdles Wednesday after two Senate committees postponed consideration of her nomination.

White House press secretary Jen Psaki told reporters that Tanden and the White House had been in touch with senators and advocacy groups to answer any questions they may have on her nomination.

“We're fighting for her nomination," she said. “She's an expert whose qualifications are critical during this time of unprecedented crisis."

Two Senate panels slated to vote on Tanden's nomination, the Homeland Security and Governmental Affairs Committee and the Budget Committee, both postponed business meetings scheduled for Wednesday, the latest signal of the challenges Tanden faces in her confirmation fight.

Tanden’s nomination ran into trouble soon after Biden announced it, and her confirmation was thrown into doubt over the last week after Democratic Sen. Joe Manchin of West Virginia said he could not support her, citing her controversial tweets attacking members of both parties.

Tanden needs 51 votes in an evenly divided Senate, with Vice President Kamala Harris acting as a tiebreaker. That means the White House can't afford to lose another Democratic vote, and one key centrist Democrat, Arizona Sen. Kyrsten Sinema, has yet to announce her position on Tanden.

And without Manchin’s support, the White House has been left scrambling to find a Republican to support her.

After three key moderate Republican senators said in recent days they would vote against her, the White House has faced daily questions about Tanden's path to confirmation. Asked Tuesday about the prospects of Tanden winning Senate confirmation, Biden said, “We’re going to push. We still think there’s a shot, a good shot.”

Psaki described the challenge facing Tanden as a “numbers game” and suggested the White House is still looking for a Republican to support her nomination. Asked whether they had looked at a replacement for Tanden, Psaki said "that's not the stage we're in.

Sen. Lisa Murkowski, a moderate Republican from Alaska who could provide the key GOP vote Tanden will need, also has not said which way she is leaning.

Lawmakers have based their objections to Tanden mostly on sharp tweets she sent in the past that caustically criticized both Republican and Democratic lawmakers.

Tanden worked for Hillary Clinton and leads the Center for American Progress, a liberal think tank. She is the daughter of immigrants from India and would be the first woman of color to lead the White House budget office.

She has apologized and deleted many of the tweets.