The working assumption is that they canned him for his “Waterloo” piece about ObamaCare and the GOP. Did they? Hmmm:

Frum made clear in a letter to AEI President Arthur Brooks that his departure after seven years at the conservative think tank was not voluntary. “I have had many fruitful years at the American Enterprise Institute,” he wrote, “and I do regret this abrupt and unexpected conclusion of our relationship.” AEI did not comment immediately.

In a brief interview, Frum said “there was no suggestion by AEI” that his sharp criticism of the GOP’s health-care strategy was the reason for his dismissal. He declined to say what Brooks had told him.

“They invited me to remain associated with AEI on a non-salaried basis,” Frum said, and he declined.

Reminds me of when a team doesn’t want to re-sign one of its free agents, but rather than risk the bad PR of simply walking away, they offer him a new contract with a pay cut so that he’ll feel insulted and walk away himself.

Then again, sometimes a pay cut is just a pay cut:

Frum says AEI president Brooks at lunch today actually lauded him for making so much noise with [the Waterloo] post.

“He said the thought might occur to me that this had to do with that,” Frum says. “He wanted to ally my anxieties on that score. He was very empatic.” Frum adds that Brooks said he “welcomed and celebrated” the debate he’d stirred up.

“He asked me if I’d like to work for AEI on a non salary basis,” Frum added. “He said it had nothing to do with my work and that after all these are hard times.”

Curiously, Frum didn’t mention any of that in his post announcing the AEI split. I’m inclined to think that it really is purely financial, if only because AEI surely knows how this looks coming so soon after the “Waterloo” column. If they didn’t have to do it for their bottom line, they’d have been much better off keeping him on staff for, say, six more months and then quietly letting him go. As it is, the left’s going to turn him into a conservative martyr — which, ironically, will be very good for Frum’s own bottom line. So, case closed? Nothing to see here? Not so fast. Here’s Bruce Bartlett, who’s become almost as relentless a critic of conservatives as Sullivan, on the split:

Since, he is no longer affiliated with AEI, I feel free to say publicly something he told me in private a few months ago. He asked if I had noticed any comments by AEI “scholars” on the subject of health care reform. I said no and he said that was because they had been ordered not to speak to the media because they agreed with too much of what Obama was trying to do.

It saddened me to hear this. I have always hoped that my experience was unique. But now I see that I was just the first to suffer from a closing of the conservative mind. Rigid conformity is being enforced, no dissent is allowed, and the conservative brain will slowly shrivel into dementia if it hasn’t already.

Etc etc. All I can say is, I hope it’s not true. As irritating as Frum can be — and he can be very irritating — most of his policy positions, as far as I know, are reliably conservative. True, he’s a fan of RomneyCare, but then, er, so is the guy who’s at or near the top of the polls right now for the GOP nomination in 2012. And yes, I know, it’s predictable that a Chamberlain-esque RINO candy ass such as myself would defend a guy who whines about Rush Limbaugh at every opportunity, but Bartlett’s point about rigid conformity is well taken. Frum’s still a hawk, at last check; he was a McCain voter in 2008 and prefers market solutions in most cases, from what I know. He’s wrong about the GOP having mishandled O-Care and he’s annoying with his endless scolding of right-wing media, but hopefully it’s still possible to be a conservative who’s wrong (occasionally) and annoying (frequently) and nonetheless employable by a conservative think tank. Currently AEI has as a fellow one of the geniuses who helped craft McCain-Feingold. Ornstein’s conservative enough, but not David Frum?

And yes, of course, AEI should be free to employ whomever it wants. Doesn’t mean they should be free from criticism, though, assuming that the suspicions about their motive here are confirmed. Oh, and a reminder to the media, which is surely polishing Frum’s new halo as I write this: When it comes to excommunicating conservatives, he knows whereof he speaks.

Update: Like I was saying about that halo. From Frum’s Twitter feed…

No, I am not going on Countdown tonight. They kindly invited me, but no.