Donald Trump’s criminal trial, soon to enter its fifth week, has felt like drawn-out foreplay. There have been moments of frisson. But as with any such encounter that stretches on and on, arousal waxes and wanes, prompting a few fateful questions. Where is this going? Hurry it up already? Ultimately, climax in this trial will depend on the testimony of one man: Michael Cohen, Mr Trump’s former lawyer. And he is not due on the witness stand for several days yet.