D.C. Council member Tommy Wells (D-Ward 6) had his “Et tu, Brute?” moment earlier this week.

The first wound landed Monday, in a late-night meeting in D.C. Council Chairman Kwame R. Brown’s office, where Brown told Wells he would be losing his powerful post atop the Transportation and Public Works Committee.

Wells, who had escorted Brown through his ward during a hard-fought chairman’s race last year, at first thought Brown was joking, according to people with whom he has discussed the meeting.

But Brown wasn’t kidding. Wells walked out of the meeting, and his colleagues finished the job the next day, voting 12 to 1 to endorse the unprecedented show of a chairman’s power.

If you’re the credulous type, you might think Brown’s decision to strip the transportation panel was an attempt to “effectively consolidate areas of similar interest,” to repeat Brown’s own rationale. That’s weak sauce, of course — whatever advantages consolidation might bring are more than offset by the considerable disruption caused by forcing members and staff to learn about city agencies from scratch.

That leaves the obvious explanation: that it was a fit of political pique, which Brown, as chairman, happens to be entitled to.

The explanation is pretty simple: By giving Wells the committee he so desired earlier this year, Brown (D) thought he was securing a reliable ally. Wells has not been a reliable ally.

Sure, Wells thoroughly investigated the infamous taxpayer-funded SUVs Brown had ordered, but he also crossed swords with Brown on various budget matters — orchestrating, for instance, the end of the non-District municipal bond exemption, which has been a thorn in Brown’s side.

To get all Dan Rather-folksy on you: Wells didn’t dance with the one who brung ’im.

Brown might not have had the opportunity to deliver such swift payback, but Harry Thomas Jr.’s abdication of the Economic Development Committee opened a door and Brown stepped right through.

Lament it if you want, but in politics, loyalty is just about all — especially in legislatures. If Wells was looking for loyalty from his colleagues, he couldn’t command any, starting with his supposed progressive ally Mary M. Cheh (D-Ward 3).

Without Cheh’s assent, Brown couldn’t have pulled off his shuffle. Cheh appears to have seen the opportunity to control a larger chunk of the budget, shepherd city transportation projects and escape the drudgery of government operations work. She took it.

Wells has spoken occasionally of leading a council “progressive caucus,” a bloc of votes to support good government and innovative policy to counteract the council’s old-school, back-slapping, glad-handing majority. Central to that alliance was Cheh and Muriel Bowser (D-Ward 4), both of whom improved their own statures at Wells’s expense.

Consider the alliance broken. Told Tuesday morning that Wells and his “livable, walkable” philosophy have a devoted following among young progressives, Cheh said, “That’s a slogan. . . . I’ve passed major legislation. I’ll say ‘livable, walkable.’ If I say it enough, will that be okay?”

Cheh has made immediate efforts to prove her progressive bona fides, dropping in Wednesday on a meeting of the city’s Bicycle Advisory Council. Bowser, meanwhile, now has the helm of Cheh’s old Government Operations Committee and is in a prime position to make a name for herself on good government. She’ll have the job of pounding a pair of imperfect ethics bills — one introduced by Brown and Cheh, the other by Vincent Orange (D-At Large) — into something resembling real accountability. And Brown did no favors for ostensible ally Mayor Vincent C. Gray (D) by appointing the longtime ally of Adrian M. Fenty to dig into executive operations.

The most unsettled question is whether Brown’s power move actually improves his own political standing.

He takes a short-term publicity hit, no doubt, reminding voters of the SUV issues and the criminal investigation into his 2008 campaign. Over the medium term, he has upped his influence with Bowser and Orange, who gets a new Small and Local Business Development Committee, maybe helping him push through those close votes where he couldn’t count on Wells.

But in the long term, who knows? Brown has probably made an enemy out of Wells, who has a smaller oversight portfolio to deal with and more time on his hands, now that he won’t be spending his Thursdays in Metro board meetings. So far he has not been too shy about playing the martyr: “I’m consistent on ethics and good government,” he told reporters earlier this week. “That may make some of my colleagues uncomfortable.”

The way things are going in this town, Brown might yet be haunted by a one-man progressive caucus.