(CNN) The pressure is mounting for Democrats to remain united on nominees moving through the Senate, as Republicans signal a growing resistance to backing some of President Joe Biden's picks for key domestic policy posts.
The nomination hearings of California Attorney General Xavier Becerra to lead the Department of Health and Human Services and Rep. Deb Haaland to lead the Department of Interior came Tuesday at a moment when the fragility Democrats' narrow majority and their ability to swiftly advance Biden's Cabinet was coming into focus. Without Republican support, Democrats need all 50 of their members to back a nominee.
With Neera Tanden's nomination to lead the Office of Management and Budget hanging by a thread since Sen. Joe Manchin, a moderate Democrat from West Virginia, announced his opposition, many Republicans believe they have more leverage than ever to potentially sink some of Biden's nominees or at the very least use the next several weeks to draw out stark policy differences between the two parties on energy, health care and abortion.
"I think this is where our Republican colleagues highlight their ideological issues and they diverge more here than on more of the foreign policy issues," said Sen. Bob Menendez, a Democrat from New Jersey. "This is where they want to drive their messaging and their arguments. They use their domestic policy nominees as the vehicle for them to do that."
Unlike a slew of national security nominees that sailed through the confirmation process and earned overwhelming support in the early days of Biden's presidency, candidates to lead agencies like Health and Human Services and the Department of Interior are meeting stronger headwinds from outside groups and conservatives at the Capitol.
"It's not some sort of concerted effort," said Sen. John Kennedy, a Republican from Louisiana. "We haven't had discussions that I am aware of about any kind of strategy. I think most people were just considering the nominees on the merits and letting the chips fall where they may."
Democrats argue it's not uncommon for the first nominees in an administration to move more quickly and smoothly, but given Democrats have no margin for error, the fights over nominees are shaping up to be closer calls than some past administrations.
"Broadly speaking over the brief decade I have been here, the national security nominees -- whether it is Secretary of Defense or the Attorney General -- get a greater degree of deference because there is more of a bipartisan sense of the urgency of allowing a president to choose their own nominee than do the domestic policy ones," said Sen. Chris Coons, a Democrat from Delaware.
The Biden administration hasn't lost a single nominee yet. The White House has been clear it stands by Tanden's nomination and Sen. Lisa Murkowski, a Republican from Alaska, has left the door open to backing Tanden, telling reporters Tuesday she wouldn't make a decision until after the Budget and Homeland Security committees voted Wednesday to advance the nomination.
But Tanden's struggle to win support in the Senate while unique given her history of tweets attacking Republicans, is also a reflection of just how narrow the majority for Democrats is. Democrats cannot afford defections in their own party and if they happen, they need Republicans to make up the difference, something that is harder to find with some of Biden's latest nominees.
At the start of Becerra's confirmation hearing Tuesday, top Republican Sen. Richard Burr of North Carolina, said bluntly: "I am not sold yet."
"I am not sure you have the necessary experience or skills to do the job at the moment," Burr said.
Sen. Mitt Romney, a Republican from Utah where public lands issues have become a political lightening rod in recent years, said he wasn't sure if Haaland was the right person for the job.
"I voted for almost all of the President's nominees so far, but Congresswoman Haaland and Neera Tanden present some real questions and challenges," Romney said.
Manchin, the chairman of the Energy Committee, has also not said if he will back Haaland, who was supportive of the Green New Deal when she was in Congress, a policy that Manchin himself is not supportive of.
"We have to finish up the hearing," Manchin said. "I think she's been doing fine."
Sen. Kyrsten Sinema, a moderate Democrat from Arizona, has also not said if she would back Haaland or Tanden.
The next several weeks could be a test of whether Democratic leadership can hold the caucus together as Republican attacks on nominees ramp up and fewer Republican votes are available to bolster Democratic defections.
"It is a narrow majority, 50/50 is pretty tight," Sen. Thom Tillis, a Republican from North Carolina, said of the delicate math.