It's a nice catch, but I disagree with Frum's interpretation, which is that it shows Perry isn't a very serious candidate, which I think means Perry is either lazy or over his head.
I'd go in another direction: Perry is confronted with a tough problem, and is taking a sensible way out. The tough problem is that doing policy in the GOP nomination contest is almost impossible. What motivates Tea Partiers and other enthusiastic primary voters? A lot of it is mythical, such as the immanent Obamcrackdown on fracking seen here, or Obama's apology tour, or Obama's plans to seize everyone's guns, or all those IRS agents that Jon Huntsman was complaining about in last week's debate. Others are internally contradictory; good luck proposing a budget that eliminates the deficit, cuts taxes, and doesn't cut spending on the military or current Medicare or SS payments. Still others are massively unpopular general election positions; that part is normal in all presidential nomination contests, but particularly an issue this time around. And hanging over all of it is the possibility that something on the approved list today could be the mark of a RINO tomorrow (see: Mitt Romney, health care reform). Not to mention that there are a half dozen or so "candidates" who are prone to making up stuff intended to ingratiate themselves to the crazies (well, it's really mainly three -- Newt, Bachmann, Cain).
It's not Rick Perry and Mitt Romney who aren't serious; it's the party they're trying to lead.
That's probably right for the most part. The GOP was not serious at least for a while before Perry and Romney decided to run for president. And they would risk losing support if they tried to be serious. But its not certain they would lose support among the base, or with the party leaders.
Romney's support seems to be evidence that both a significant portion of Republicans and the party leaders value someone who can be serious. Perry's decline in support seems to suggest that a candidate needs to have some aura of seriousness. Cain's rise suggests a significant portion is either easily fooled or doesn't value seriousness. But at least they aren't crazy enough to support Gingrich, Bachmann, and Paul.
Just as I typed that I think I convinced myself that the Republican party, or at least its leaders, aren't as crazy as they appear. And let's be real about Cain, its highly unlikely his support will last long. So its likely that they will nominate Romney, someone who has shown the ability to be serious. And remember just a few years ago when they nominated McCain, who also had displayed moments of seriousness.
I started this post wanting to talk about how GOP candidates and office holders help perpetuate the crazy inhabits their party and forces them to be un-serious during debates and when talking about policy. I'm not sure someone like Perry or Romney could change that fact too much. But I think they could help a little if they were serious and didn't completely pander to the crazy, or mythical as Jonathan puts it. But what I've convinced myself of is that while the rhetoric and proposals going around right now aren't very serious, the act of actually choosing the candidate seems to be a serious endeavor on at least some level. Otherwise I don't think Romney would get so much support while the really crazy candidates basically get none (Cain's current rise notwithstanding).
My hope is that once Romney gets the nomination he stops pandering to the crazy and taps into that seriousness that helped him get elected governor of a liberal state and enact serious policies. And if the economy is still isn't noticeably improving and Romney wins, I hope he governs in a serious manner and helps delude some of the crazy that has come to the forefront over the past few years.