A razor-tight Senate margin is complicating President-elect Joe Biden's strategy for filling his Cabinet by making it more difficult to pick sitting lawmakers for plum posts.

Normally, members of Congress would be at the top of the list for an incoming administration looking to poach talent from the party's ranks on Capitol Hill.

But with Biden wanting to move fast and control of the Senate in limbo until early next year, he’ll have to think twice before tapping congressional Democrats — a move that could open up a seat for Republicans to try to flip or tip the scales in a closely divided Congress.

“I think the vice president understands that politics is a game of addition and multiplication, not subtraction and division,” said Democratic strategist Antjuan Seawright.

“I can’t see a scenario where [Biden] will risk losing numbers in the Senate that he would need to deliver an agenda that is so critical,” he continued. “You could argue the same point with a swing-district member of Congress.”

Democrats in both the House and Senate are looking at thin margins that could make it difficult to justify picking a member of Congress for a Cabinet position if it risks depleting the party’s ranks or setting up a special election in a red or purple state.

Republicans are poised to enter January with 50 Senate seats to Democrats’ 48 seats. Which party will control the majority will come down to two Jan. 5 runoff elections in Georgia. If Democrats win both they will have the majority because Vice President Harris could break a 50-50 tie. Even if they lose one or both, the GOP majority will still be capped at 51 or 52 seats.

In the House, Democrats are seeing their majority whittled down to the low 220s with Republicans viewing the slimmed-down majority as a chance to squeeze Democrats on procedural votes like motions to recommit, where they’ve had success getting moderates to break ranks.

Sen. Ben Cardin (D-Md.) caveated that the potential blowback of picking a senator was speculative, because it depends on what happens in Georgia, but “I think that’s an issue that President-elect Biden needs to consider.”

“It might be a zero-sum game so it may not make any difference as far as the control of the Senate is concerned,” Cardin said. “Everything else being equal, senators have been in Cabinets and they’ve done great jobs.”

Asked about picking senators, Sen. Tom Carper (D-Del.), a close Biden ally, said that “there are good reasons to choose senators, many of them are experts in different parts of policy.”

But pushed if doing so could risk opening up a seat, Carper added with a laugh, “you have to be very careful.”

“You have to use some judgment. Some discretion would be called for,” Carper said.

Spokespeople for Biden’s campaign and transition team didn’t respond to questions about potential Cabinet picks.

Several senators are being publicly discussed for positions, a move that could set off a game of musical chairs if they are picked.

Sen. Chris Coons (D-Del.) is being floated as a potential secretary of State for Biden, whose Senate seat he holds. Coons, a member of the Foreign Relations Committee, is frequently discussed as being in the mix along with former Ambassador Susan Rice and former Deputy Secretary of State Tony Blinken.

Coons could be easier to confirm in a Republican-controlled Senate because he’s widely respected in both parties. But in a narrowly controlled Congress, Coons could also be an asset to Biden in his current post because of those same deep ties with GOP senators.

Coons, during a recent ABC News interview, made it clear he is interested, saying, “I’d be honored to serve.”

Coons comes from a safely Democratic state. Under Delaware law, a vacancy would be filled by Democratic Gov. John Carney and his successor, if he’s picked, is widely expected to be Rep. Lisa Blunt Rochester.

Biden has been in touch with Senate Minority Leader Charles Schumer (D-N.Y.) since winning the White House race, but the two have not discussed the potential that the president-elect could pick members of the Democratic caucus to join the administration. Asked about the possibility, Schumer told reporters that Biden “has not consulted me on that issue.”

Sen. Chris Murphy (D-Conn.), whom progressives are championing as a secretary of State pick, noted that rules for replacing senators vary by state and that he’s “sure the president-elect will take that into consideration,” but that Biden “should have the broadest pool of applicants, or choices, at his disposal as possible” including senators.

“I want President-elect Biden to pick the best people and if there are people who he thinks can serve him who are in the Senate, he should have the right to make those choices,” Murphy said.

Other potential picks could risk opening up seats that Republicans could either appoint a member of their party to or risk giving Republicans a pathway to flipping a seat in a special election.

“It depends on the state and how the appointment process works, but in a state with a Republican governor, you run the risk of losing numbers,” Seawright said.

Sens. Elizabeth Warren (D-Mass.) and Bernie Sanders (I-Vt.) are both being pushed by progressives as picks to lead the Treasury and Labor departments, respectively. 

But if Democrats control the chamber in a 50-50 tie, nominating either could give GOP governors in both states an opening to appoint their successors and flip control of the narrowly divided Senate.

Sen. Pat Toomey (R-Pa.), asked about if he could support Warren for Treasury Secretary, cast doubt on Biden picking her because of the Senate implications.

"I doubt very much that Secretary Warren would be on the nominating table because the governor of Massachusetts is a Republican and replacing her with a Republican senator probably wouldn't go really well with Senator Schumer," Toomey said during a Washington Post Live interview.

In a potential de-ecalation of that risk, a Democratic state representative in Massachusetts already proposed a budget amendment to alter the appointment process by requiring the governor to appoint an interim replacement of the same party as their predecessor. And in Vermont, GOP Gov. Phil Scott said late last month that he anticipates he would look at a “more left-leaning type of independent that would obviously caucus with the Democrats."

If Republicans control the Senate the risk could be twofold: Though the majority wouldn’t hang in the balance it would give Republicans a chance to strengthen their hold on the chamber. It would also risk either giving up a Senate seat only to be rejected by Republicans.

“McConnell is never going to let a progressive like Elizabeth Warren become Treasury Secretary,” a Democratic strategist said about Biden’s picks.

Senators from states with Democratic governors are also reportedly under consideration, including Sen. Amy Klobuchar (D-Minn.), who is up for reelection in 2024. 

While Biden carried Minnesota in the election, Republicans have increasingly turned their sights on the state. Democratic worries bubbled up late in the 2020 cycle that Biden or Sen. Tina Smith (D-Minn.) could be vulnerable in the state, prompting a last-minute campaign stop from Biden. Republicans also control the state Senate.

Klobuchar told CNN shortly after the race was called that Biden had not spoken to her about a Cabinet position, adding that “I think part of that is that I made clear, I like what I'm doing and I think it is a very critical role right now."

Safer picks for Biden from the Senate could be retiring lawmakers.

Sen. Tom Udall (D-N.M.) is under consideration to be Interior Secretary and Sen. Doug Jones (D-Ala.), who lost his November election, is also in the mix for Biden’s attorney general spot.

Asked this week, Jones didn’t rule out accepting an administration post.

“I want to see the Biden-Harris administration succeed, I really do,” Jones said. “If I can contribute, great, but you know we'll see how it goes.”