Joe Biden’s team is considering an informal ban on naming Democratic U.S. senators to the Cabinet if he wins — which would effectively block Elizabeth Warren for Treasury or Bernie Sanders for Labor — people familiar with the discussions tell Axios.

The big picture: Biden, if he wins, is bracing for bruising legislative battles on day one, starting with the next phase of coronavirus relief. Many advisers don’t think he can afford to lose a single vote in the Senate if Democrats hold a slim majority.

• Biden himself hasn’t made a decision on a potential Senate ban, with his efforts focused on winning on Tuesday, the sources say.

The intrigue: An informal ban could also be an elegant way of tamping down campaigns to place progressive senators in top Cabinet roles by reminding the movement of the priority around enacting legislation.

• Warren and Sanders both come from an unusual construct — blue states with Republican governors who'd be empowered to fill vacancies.
• There might be a way for a Democratic supermajority in the Massachusetts legislature to force Gov. Charlie Baker to appoint a Democrat. That looks less likely in Vermont where Gov. Phil Scott is expected to cruise to re-election.

Be smart: Progressives are trying to build momentum for Warren and Sanders, to press a prospective Biden administration to embrace economic justice and eschew traditional special interests.

• Some members of Biden’s inner circle are deeply skeptical about handing Treasury, which will play a key role in any economic recovery to Warren, who has expressed interest in the job.

Between the lines: If strictly applied, an informal ban also would dash Cabinet hopes for senators from states with Democratic governors, such as Chris Coons, Tammy Duckworth, Amy Klobuchar and Chris Murphy.

• Biden is close to several of them and would have to gently tell them their services are needed more in the Senate.

But, but, but: If Democrats can secure a comfortable margin in the Senate, there’s less of an argument that losing a single seat would crimp Biden’s agenda.