There is a small but significant distinction in politics between what is known and what is declared. In recent weeks it has become ever harder to imagine how Theresa May might continue in her job if another attempt to steer Brexit through parliament fails. But imagination is no longer required. Resignation terms have been negotiated with the backbench 1922 Committee, and made public.

After a second reading of the EU withdrawal bill, scheduled for the first week of June, May and Sir Graham Brady will draw up a timetable for the election of a new Tory leader.

It has also not required a great leap of imagination to suppose that Boris Johnson fancies his chances in that contest. But it is still noteworthy that he stopped being coy today. “Of course I’m going to go for it,” he told an audience in Manchester. The state of being talked about as an inevitable candidate and actually running are different, partly because of the cascade of questions that follow. For other MPs it is no longer a matter of “could you support” but “do you support”. For other candidates there is added pressure to make implied ambition more explicit.

And while little of substance appears to have shifted, the political narrative unfolds in a different tense, no longer “would” but “will”. Given the suffocating stasis that has afflicted Westminster politics in recent weeks, that counts as movement. For May the hope is that the certainty of a leadership contest, combined with terror at the expected success of Nigel Farage’s Brexit party in next week’s European parliamentary election, will persuade Tories that their interests are served by nudging the EU withdrawal agreement closer to enactment. It is a straightforward transaction. She gets something to feasibly call a legacy – a consoling moment in which it can be said that the one job she ever really had to do has been done. The party then gets to argue about how swiftly to move on from her legacy and who should have the honour of trashing it.

‘Boris Johnson has stopped being coy. ‘Of course I’m going to go for it,’ he told an audience in Manchester.’ Photograph: Reuters

That some Tory MPs are up for such a bargain was demonstrated when the Commons voted on May’s deal on the 29 March – the last day of the original article 50 negotiating period. It was another defeat for the prime minister, by 58 votes. But there was a discernible shift in mood on the Tory benches as a number of Eurosceptic ultras – including Jacob Rees-Mogg, Johnson and Dominic Raab – talked themselves into tactical alignment with Downing Street. Their argument, spelled out unambiguously in the Commons debate, was that the benefits of legally severing ties with the EU outweigh the costs of doing so on shabby terms. Brexit itself was imperilled by the machinations of remainers and so the priority was getting through the only visible exit door. All other considerations could then be dealt with on the landing.

That argument might have even more purchase with Conservatives now that the electoral consequences of Brexit delay have been made brutally clear. Given what happened in local elections earlier this month and what is expected in the MEP ballot next week, a rational evaluation of the Tories’ collective prospects suggests the party should set aside any reservations about May’s deal, stick a bow on it and offer it to the nation as the gift of freedom. But rationality has not been a conspicuous motive at the fanatical end of the Eurosceptic spectrum. There is a hard core of MPs who will not besmirch the ideal of total liberation from Europe by engaging in grubby tactical voting for a partial version.

Besides, nothing repels Labour’s pro-Brexit MPs quite like the sight of Tories backing May with fingers ostentatiously crossed – plainly intending to pursue a more extreme agenda under a more radical successor. If Johnson is on board, Labour leavers jump ship. So the task of assembling a parliamentary majority in a fortnight is not that much easier than it was last time, or the time before, or the time before that.

Only one thing has changed: the Conservative party no longer has to imagine the circumstances in which the prime minister stands down. It is no longer a hypothetical event but a certainty of the political calendar. May was due to face a confidence vote of local party associations on 15 June and the near certainty of humiliation has surely helped set the deadline for her resignation. The moment is now inked into Tory diaries for early June, alongside a set of calculations about who is backing whom in the subsequent leadership contest. The prime minister herself might still be thinking in terms of a legacy, how she might be remembered in the future, but everyone else in British politics from now on talks about Theresa May in the past tense.

• Rafael Behr is a Guardian columnist