I don't know Frum personally, and he's not in my field. But two reasons to wade briefly into this scrum are (a) I've spent some time at AEI, though not much recently, and (b) I have some familiarity with the people involved in the subsidiary scrum, relating to Bruce Bartlett's assertion that Frum told him AEI was muzzling its healthcare scholars because they were too supportive, for its politically directed tastes, of the Obama healthcare plan.
Some rebuttals of the claim that AEI could have been muzzling its healthcare scholars note that, for example, Glenn Hubbard has frequently and recently opined in print about healthcare reform. But, while Glenn has a long history of writing about healthcare in relation to the fiscal system, he would not have been among the people Frum would have had in mind. I won't name AEI's healthcare specialists here, but you can find their names on the AEI website, and I don't think they've had much to say publicly on the topic in the last couple of years, which is interesting and indeed surprising.
I'd also note that (a) when I met and talked with these individuals in connection with my Medicare book, it was clear they are serious people and straight shooters, not political hacks, (b) I would be surprised if they were NOT sympathetic to the approach of mandating health insurance coverage, given this idea's deep roots in (without restriction to) conservative, Republican, and generally pro-market circles, along with the fundamental argument in support of the mandate as a response to adverse selection (a central problem in promoting the general availability of adequate medical treatment).
In short, I see a compelling circumstantial case in favor of the claim of muzzling that Bartlett reports.
Just as we need two responsible political parties in order to address big problems like the fiscal gap, so we need reputable and independent think tanks across the political spectrum, developing and debating alternative approaches with reasonable honesty and openness (although of course they can't be interchangeable with academic institutions if they are relying on funders to advance particular ideological stances). AEI has often had one foot in the reputable camp - it has in fact sponsored a lot of genuine and excellent scholarship over the years - and one foot in the camp of hiring political operators to make party line statements. Sometimes even particular individuals step at different times into both pools (if I may change my metaphor).
When AEI fires Frum right after his recent controversial remarks, and possibly (though I realize this remains unproven) sets about muzzling good experts, while also hiring a few too many rancid and rabid hacks (even if an occasional one comes with the territory), it slaps in the face the reputable people who continue to work there. Sure, maybe they should consider leaving, but that's easy for us to say. Opportunities aren't infinite, indeed sometimes they're scarcely even finite. AEI and its legitimate scholars have been members in good standing of a broader, ideologically diverse community of experts in various fields. And whatever the other incentives that AEI might face, it is hurting itself, good-faith versions of the ideas it espouses, and the broader policy process if it throws this away in the pursuit of enforced political orthodoxy.