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. Vermont Gov. Phil Scott said on Friday that if Sanders joins a potential Biden administration, he would consider a "more left-leaning type of independent that would obviously caucus with the Democrat" to replace him.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.Editor's note: This post has been updated with a quote from Vermont Gov. Phil Scott.