And Tory members of Parliament who support a cleaner rupture with Europe are submitting letters saying that they have lost confidence in Mrs. May, which could very soon trigger a vote on her future.

Mrs. May has weathered crisis after crisis as prime minister. But commentators say she has never looked as alone as she does now.

There’s little chance the deal gets through Parliament.

The agreement, struck between negotiators in Brussels and Mrs. May’s government, faces a long road ahead, even if Mrs. May manages to hold on to her job.

The first stop (if it gets that far) is a summit meeting of European Union leaders on Nov. 25. The deal has their support, and it will ultimately need the backing of the European Parliament.

More troublesome is a mid-December vote by the British Parliament, which also gets a say on the agreement. Mrs. May needs 320 votes there for a majority. By one estimate, she will have to cobble together about 85 of those from members of the opposition Labour Party and deeply skeptical allies.

The problem is that a divided country has finally been united — in disliking the deal.

For those who want Britain to remain in the European Union, the deal is worse than staying in the bloc under the current terms, because it forces Britain to adopt European trading rules without having a say in what they are.

For those who want to sever ties, it’s worse than a clean split from the European Union, because the agreement could trap the country in a regulatory system it can’t unilaterally leave.