You likely remember the 3 a.m. phone call.In 2008, the most effective line of attack his opponents mounted against candidate Barack Obama centered on the freshman senator's lack of experience. An ad for Hillary Clinton famously implied that you did not want this callow naif answering the phone at a moment of pre-dawn crisis.Though the country eventually decided it did, in fact, want Obama, the argument was valuable in that it forced the electorate to ask itself what kind of experience is necessary to a president. There is a corollary question that becomes more obvious and urgent with each passing day. It involves not quality of experience, but quality of mind.On Monday, an editorial in the Manchester (N.H.) Union Leader attacked Herman Cain for blowing off an interview with the paper. It seems that after video of Cain stumbling to articulate a position on Libya in an interview with the Milwaukee Journal Sentinel went viral last week, the candidate instituted a new rule: no video cameras in newspaper interviews.A spokesman for the Cain campaign said this was because “videos are typically used for television and it's a newspaper.” But as the editorial noted, videos are used for pretty much everything these days. It suggested Cain's real problem lay not in the presence of cameras, but in the fact that “newspaper interviews tend to be longer and more in depth” and require answers that go beyond canned soundbites. Cain's refusal to engage in that sort of rigorous give and take, said the paper, “gives the impression that he's got something to hide.”Cain capitulated that same day.But the damage is done. The attack solidifies a perception that he does, indeed, have something to hide, i.e., the fact that once you get him past his talking points (”9-9-9” and fences to electrocute unsuspecting Mexicans) — he really has nothing to say.That has become a disturbingly common thing in recent years. Sarah Palin considered “What do you read?” a gotcha question. Michele Bachmann thinks HPV vaccinations cause brain damage.Now comes Cain mangling a basic question about foreign policy. He has claimed he simply paused to gather his thoughts, but anyone who has seen the video knows better. In his painful hemming, hawing and false starts, Cain comes across like a fifth grader called up to the blackboard and wishing he had studied the night before. This is the same Cain who asked how to say delicious “in Cuban” while at a restaurant in Miami, the same Cain who spoke of the need to keep China from developing nuclear capability — which China did 47 years ago.A presidential campaign constitutes the world's longest and toughest job interview. While it's fine to vet candidates on likeability, credibility and, yes, experience, it might not hurt to require that they also show evidence of having thought deeply and with an informed mind about the world and America's place in it. We are, after all, choosing a president — not a golf buddy.One sometimes wonders if some of us know the difference. That Cain stumbled so badly on a routine question does not speak well of his intellectual firepower.That he is a leading candidate for the presidency does not speak well of ours.