I understand the appeal of Herman Cain, who seems like a likeable and engaging man. He’s someone who has an impressive business history. He can also be quite strong when refuting the smears of people like Cornel West and Harry Belafonte. And there’s no doubt he’s helped himself in the presidential debates, much like Mike Huckabee did in 2008. But when the dust finally clears, I find it hard to believe Cain will win the GOP nomination.

Part of the explanation is that the presidency is not, in the words of Richard Brookhiser, “an entry-level position.” Beyond that, Cain is notably unknowledgeable and seemingly not curious about national security matters. He has demonstrated that weakness several times, including his cluelessness in interviews  about the issue of the Palestinian “right of return,” in debates about our military strategy in Afghanistan, and in his knowledge of what he (kiddingly) calls “Ubeki-beki-beki-beki-stan-stan.”

Let’s stipulate that many people who run for president (especially governors) aren’t always well-versed in foreign policy matters. And let’s stipulate, too, that instincts and tendencies are quite important. (For example, one may be a strong supporter of Israel without having an exhaustive knowledge of the history of the Middle East since 1948.) Still, there is a certain baseline of information one hopes to find in presidential candidates – something Cain has not demonstrated. And for all the understandable talk about the importance of economic growth, prudence in and knowledge of national security matters remain the most important qualifications for a commander-in-chief.

I’d add two other concerns about Cain. The first is that his so-called “9-9-9” plan, which would replace the current tax system with one that combines a 9 percent personal flat tax, a 9 percent corporate flat tax and a 9 percent national sales tax, has real weaknesses, including instituting a consumption tax while the federal income tax remains in place. (It would eventually finance an even larger entitlement state, as the Wall Street Journal pointed out recently.) Then there’s Cain’s insistence  he would not appoint Muslims either to his cabinet or to the federal bench simply by virtue of their faith, and his advocacy of a “loyalty proof” for Muslim-Americans.

I take the latter to be evidence of Cain’s tendency to shoot from the hip (indeed, he’s walked back a bit from his statements). At times, provocative spontaneity can seem impressive and appealing. But at other times it can raise questions about an individual’s readiness to be president. Here’s what I do know: If Cain remains a top-tier candidate, the scrutiny on him will increase in ways he cannot even imagine. His lack of command on key issues will be exposed. How well he can hold up against it is a wide-open question. But my guess is that Cain looks better now, and polls better now, than he will a month from now. I wouldn’t be surprised if this isn’t seen as the high water mark of Herman Cain’s campaign.

As a cancer survivor, he’s overcome a lot more than critical comments and negative predictions by the political class. Maybe he’ll do so again. We’ll know soon enough.