With a party conference just around the corner, Mr. Johnson is making himself available as an alternative to a large segment of the party that would see Mrs. May’s softening stance as a betrayal. “He is offering himself as a different kind of leader, who would negotiate in a different spirit,” Mr. Gimson said.

In some respects, the surprise is that Mr. Johnson — who lately has found himself in Nigeria and on a hurricane-hit Caribbean island while colleagues in London debate withdrawal from the European Union, the one policy that matters to him — has been so quiet for so long.

In recent months his low profile has taken him from leader-in-waiting to also-ran, according to one recent poll among the activists of the Conservative party who will ultimately pick its next leader. That showed him to be well behind Jacob Rees-Mogg, a caricature upper-class Conservative who is not even a minister, let alone in the cabinet.

This is where the politicking comes in. Now a pariah to pro-Europeans, Mr. Johnson undoubtedly sees that he needs to be popular among Brexit supporters if he is retain a chance of succeeding Mrs. May.

If and when that contest happens, Mr. Johnson does not need to be the leading candidate, just one of the top two chosen by Conservative lawmakers – a big chunk of whom are Brexit enthusiasts. At that point, the voting goes to Conservative Party members, who also tend to favor Brexit.

Mr. Johnson will have a chance to rally party members to his cause at next month’s annual convention, where he usually gives a humorous and rousing speech to a standing ovation. It will be a much harder occasion for Mrs. May, a poor public speaker who must explain her failure in the June election while reassuring hard-liners that she can deliver a successful Brexit.

That Mr. Johnson remains in his post is a testament to Mrs. May’s vulnerability. She knows it would take just 48 of her own lawmakers to provoke a leadership contest that she would probably lose, and Mr. Johnson has several dozen potential supporters in Parliament.