But there are degrees of ambition; and not every MP has the kind of relentless Julius-Caesar ambition that stops at nothing. Those that do, while they do, think of little else, every waking moment. Asleep, they dream about it. To the extent you can identify those ones (steam issuing from the ears is usually a sign), whenever something big goes down it's always fun to watch and to speculate how they see it; how the event impacts on them; how they try to turn it to their advantage.
It's pretty clear that the advent of elected mayors in the UK provided a form of outdoor relief for the Truly Ambitious to essay the Caesar-in-Gaul trick. First out of the blocks was Ken Livingstone, a man of boundless self-confidence and chutzpah - but the timing didn't work for him: he never stood a chance of nipping in ahead of Gordon Brown. By the time of the 2010 Labour leadership vacancy, he was pretty vacant himself, a busted flush shouting at people in the street.
Boris, by contrast, worked it all to his advantage and a couple of lucky breaks later, here we all are.
Which brings us to the current difficulties of Sir K.Starmer. Who'll be figuring out the next phase of their strategies now?
By some accounts, none other than Angela Rayner (41) works permanently and purposefully to advance her own cause. She certainly showed infinitely more fight in her own crisis than Rebecca Long Bailey in either of hers (x divided by 0 being infinity), with a gaggle of outriders in the field to cover her flanks with the meeja. (RLB had an army ready to do her bidding: but she never blew on the horn.)
But Exhibit A is Sadiq Khan. I probably don't need to convince you that he is firmly set on the Top Job. Those mayoral roles, of course, come with the perils of fixed-term schedules, but Boris finessed that by re-entering the Commons a year before his London term ended. We may confidently assume Khan expected to do the same, probably in 2023. But will he now feel that's too late? Starmer looks like he might implode before that; and in any event, Boris may pull the GE trigger before then, too. Can Khan be sure Starmer's successor will be equally short-lived in post? He's 50 now; how strong a challenge could he mount at 60, say? Logically, he has to be in Parliament no later than at the time of the next GE.
I don't think we should be surprised if he seeks a "dual mandate" (as it's known) at the first opportunity: a nice, diverse Zone 2 parliamentary seat. He's sufficiently transactional, he might even force that opportunity by getting someone to resign for him; though I'm not sure Labour Party rules would give him any certainty of being put on a by-election ballot paper, whatever the locals might want, if the Starmer machine retains executive power ... Decisions, decisions. One thing's certain: he'll be on manoeuvres at all times, and (for anyone even vaguely amused by this stuff) his public utterances should be monitored with interest. As a minimum, watch him claim titular championship of the supposed new Labour bedrock of metro-bedsits and diversities.
This all tends to make us look in the direction of Manchester to that other mayoral paragon, lovable little Andy Burnham (51). In principle, all the same structural considerations apply to him. But ... does he strike us as in the same league, ambition-wise? My best guess is that he wouldn't force the pace proactively, and is more in the "if it fell in my lap ..." category.
Any other foaming-at-the-mouth candidates we can spot in the ranks of the People's Party? And what will they be up to next?