In keeping with the White House's focus of the day, Biden held a bipartisan Oval Office meeting Wednesday with House and Senate members ahead of signing an executive order mandating a review of critical U.S. supply chains.

"The last year has shown the vulnerability we have with some of the supply chains, including the PPE that we needed badly but had to go abroad to get. And there are current strategies," Biden said.

Biden praised the bipartisan effort to address the shortage of the chips for cars and said the group planned to discuss the problem, along with other shortage issues.

-ABC News' Molly Nagle

The White House was surprised to discover that Johnson & Johnson will only have about 3 to 4 million doses of its vaccine ready to ship once the FDA grants an emergency use authorization, White House press secretary Jen Psaki said during a press briefing Wednesday.

Johnson & Johnson had estimated it could ship 12 million doses at the end of February in a $1 billion contract signed with the federal government in August.

“We were surprised to learn that Johnson & Johnson was behind on their manufacturing. As you noted, it was kind of reported earlier to be about 10 million, and now it's more like 3 to 4 million doses that they would be ready to ship next week if they are moved through the FDA process, which is not yet concluded, just to note," Psaki said. "And we are going to continue to work with them on ensuring that that can be expedited.”

Despite the initial availability, Johnson & Johnson has said it expects 20 million doses to be available by the end of March and to meet its contractual obligation for 100 million doses by the end of June.

-ABC News' Sarah Kolinovsky

Veteran diplomat Linda Thomas-Greenfield was sworn in Wednesday morning as Biden's U.N. ambassador. Thomas-Greenfield, known for her "gumbo diplomacy", is a Louisiana native and child of the segregated South.

After being sworn in, Thomas-Greenfield tweeted saying she was "honored" to hold the post.

"Diplomacy is back. Multilateralism is back," Thomas-Greenfield said in the tweet. "America is back."

White House press secretary Jen Psaki was asked during a press briefing Wednesday whether the postponement of Senate hearings for Biden's pick to manage the Office of Management and Budget was a setback and Psaki said she wouldn't "put it in those terms."

Psaki emphasized that the administration is still "fighting" for Tanden's nomination and remains committed to getting Biden's pick confirmed. When asked whether Tanden had offered to withdraw her nomination, Psaki said that is "not the stage" the administration is in.

"The stage we’re in is working to continue to fight for her nomination. And, as you know, it’s a numbers game, right? It's a matter of getting one Republican to support her nomination," Psaki said. "We're continuing to do that outreach, answer questions they have, and continue to reiterate her qualifications."

Sen. Richard Shelby, R-Ala., a top Republican on the Appropriations Committee, is throwing his weight behind an alternative nominee to head the Office of Management and Budget: Shalanda Young.

Young was nominated by Biden to be deputy director of the Office of Management and Budget. Young was most recently the staff director at House Appropriations, and she and Shelby have a close working relationship.

“I believe she would be good in that role. She’s smart, she knows the process inside-out, and she’s an honest broker who has demonstrated the ability to work with both sides and get things done. She would have my support, and I suspect many of my Republican colleagues would support her, as well," Shelby said in a statement. "But that’s up to the Biden Administration.”

White House press secretary Jen Psaki was asked about Shelby's support on Wednesday and the possibility of Young being a Neera Tanden replacement, but she made clear that the White House maintains support for Tanden.

-ABC News' Trish Turner