I can't be the only person who is confused by Theresa May's appointment of Boris Johnson to the Foreign Office. I am sure that the Foreign Office is too, for a start.
It is clear that May has decided that those who proposed Brexit should manage its consequences (Prite Patel, maybe, apart) and that Johnson, who many of them would have had for leader instead of her, should be seen at the top of that group. By doing this she has made it clear that she either wants enthusiasts in these jobs or that she is setting them up to fail: it may, of course be both.
My suspicion is that she thinks that the failure will be quick, and brutal. I have a hunch she will demand pre-negotiations. She knows she won't get them. And she knows Johnson, who will not be directly involved as this will be Davis' role, will nonetheless upset a lot of people quickly and whilst this process is going on. And when they fail to deliver progress - as the EU almost guarantees they will - she will use Johnson's growing list of gaffes to say that enough is enough, call an election and expect to win on the basis of proposing to stay in after all, and make clear that she then intends to shuffle them all out.
It's a high risk strategy. It could fail miserably. But that is true of just about all the options she faces, which means she has to have a way to get to a Plan B which is what she really wants without the U-turn that this will require appearing to be her fault. Make it Johnson's instead then during a period when she thinks her only opposition is internal because Labour will be mired in a leadership contest.
I might be hopelessly wrong on this, of course. I simply offer it as a hypothesis whilst suggesting that setting people up to fail has been a strategy known for long enough to think that in the impossible position she finds herself in May have decided to resort to such an unusual approach.