This is what transpired in 2015: the Corbynistas ran amok. They swarmed to their man. Corbynmania was born. PHOTOGRAPH BY ROB STOTHARD / GETTY IMAGES

It is your tenth birthday. You invite close friends to your party, plus a few other kids from your class—the popular ones, good to have on your side, and maybe a couple of smart ones, who know all the answers to the questions. Your mother has an idea: “Invite Jerry.” You scoff at the thought. Jerry is the outlier—the class grouch, making trouble but never headway. Nobody hates him, but you all roll your eyes whenever he raises his hand, because you know what’s coming next. Plus, Jerry is no fun. He actually likes school. For just those reasons, however, your mom thinks you should include him; it will loosen the guest-list, shake things up a little. So, with a sigh, you agree.

Jerry comes to the party. Everyone laughs when he arrives—dressed like a dork, of course, because he is a dork. Still, he hangs around, and talks. And then something strange happens. The other kids begin to listen to Jerry. They sidle toward him, and cluster round. He seems different from everyone else; that used to be a liability, but now it makes him stand out from the crowd. It even makes him—get this—a little bit cool. And so it is that, as the party ends, everybody leaves with Jerry, hanging on his every word. He has already blown out the candles on your cake, taken a large slice for himself, and handed round the rest. He has opened your presents. He has utterly won over your mother, who finds him “so real” compared with the rest of your pals. Today, in short, feels like his birthday, not yours. Everybody loves Jerry.

All of which is one way of describing the events that have overtaken the Labour Party in Great Britain over the past four months—events that culminated, Saturday, in the election of Jeremy Corbyn as the leader of the party. How you regard this singular occurrence depends on your point of view. If you cleave to the idealistic left and believe that Labour has strayed for too long from the path of righteousness, you will treat the ascent of Corbyn to the top job—he is now the Leader of Her Majesty’s Opposition, in Parliament—as the advent of a Messiah. (That was certainly the tone of the adulation that Corbyn received on Saturday afternoon, in Parliament Square, when, in his first deed as leader, he addressed a large rally that was urging the government to welcome refugees who are fleeing war in Syria and elsewhere, and arriving in ever greater numbers at the borders of Europe.) If you are someone who worked for Tony Blair, when he was the party leader, you will lie down in a dark room, press your fingers to your temples, and wonder if your life’s work just got thrown out with the trash. And, if you are a member of the Conservative Party, currently governing with a healthy majority, you will solemnly pour a glass of champagne and then, midway through your first sip, start laughing so hard that bubbles come out of your nose.

Our story begins on May 8th, when the Tories, contrary to all predictions and polls, awoke to discover that they had won an outright majority in the general election. The Labour leader, Ed Miliband, resigned forthwith. An interim boss took his place, while the contest to find his successor got under way. Three candidates emerged: Andy Burnham, Yvette Cooper, and Liz Kendall. All of them were personable, well-drilled, and hovering ideologically around the center of Labour politics, with Burnham tilting slightly to the left and Kendall to the right. All three had been shadow ministers. (This means that, while your party is out of power, you “shadow” your opposite number in government, challenging his or her policies in the House of Commons and constructing better ones of your own. In so doing, you prepare for the day when, after your party wins an election, you step into the full glare of ministerial office.)

And then, unexpectedly, a fourth contender arose. His name was Jeremy Corbyn, and he was a last-minute candidate. That is no exaggeration. Anybody wishing to enter the contest for the leadership had to be nominated, with the support of thirty-five Labour Members of Parliament, by noon on June 15th; with hours to go before the deadline, Corbyn was still short of that figure, and it was not until 11:59 A.M., apparently, that the final nomination for him was registered. What movie director, making “The Corbyn Supremacy,” years from now, will be able to resist a closeup of that second hand, and its deafening tick?

One wonders how funny that film will turn out to be. The scenes set in 2015, for sure, will be tinged with irresistible comedy. We will see the faces of the actors playing Burnham, Cooper, and Kendall as word begins to filter through, from the campaign trail, that they are no longer in a three-horse race; that the hobbling outsider, far from being an also-ran, is right on their hooves. Even more aghast will be the expressions of the Corbyn nominators. It is now clear that some of them—sane, experienced politicians—encouraged him to enter the fray not because they shared his beliefs, or even because they were backing him in the leadership contest, but because they felt, in their wisdom, that the race would benefit from a broader range of candidates. The other three were on the bland side; why not, you know, toss a maverick into the mix? Who on Earth could object to a more vigorous debate? To which the only response is: be very, very careful what you wish for.

Jeremy Corbyn is sixty-six. He has been married three times. “He’s a genuinely nice guy,” according to his first wife. “The problem is that his politics are to the exclusion of other kinds of human activities.” There is a cruel caricature, hard to erase from the popular imagination, that depicts the archetypal resident of the British far left: a bearded, bicycle-riding, teetotal vegetarian from Islington, in north London. The image is lazy and unjust; in Corbyn’s case, unfortunately, it also happens to be true. Since 1983, he has been the Member of Parliament for Islington North. He owns no car. He was a member of the Campaign for Nuclear Disarmament and the Stop the War coalition against the invasion of Iraq. His natural weapons are the banner, the bullhorn, and the protest march. He has never been a minister, or a shadow minister. What he has been, persistently, is a pain in the neck, or, at any rate, a thorn in the side. More than five hundred times in his parliamentary career he has defied the whip; in other words, he has ignored the advice of the party whips—a thrillingly British term for the enforcers who, in a House of Commons debate, cajole and command M.P.s to vote in line with the leadership. Corbyn’s reputation as a rebel has been honestly earned, over the long haul, but it now presents him with a problem; how exactly, in his new capacity, can he expect those who serve beneath him to obey the touch of the whip? How do you square the example of your own conscience with the need for party order, without which, in opposition, you cannot hope to hold the government to account?