Everyone, Walker included, seems to agree the comparison wasn't well founded, but to state the obvious, it's hard to imagine this quotation being a major source of grief for him in the campaign. Operatives and reporters are in full gaffe-spotting mode already, but many of the alleged boneheaded quotes seem destined to fade. I'm so old I remember when prominent journalists were saying Walker's failure to disavow Rudy Giuliani's claim that President Obama didn't love America should disqualify him from contention. (It was last Friday.) And yet here he still is!

Shortly after that dinner with Giuliani, Walker was asked about whether he believed Obama was a Christian and said he didn't know. He tried to spin that as a response to a gotcha question, a trick that might have worked more effectively if his spokeswoman hadn't hastened to assure The Washington Post that he knew Obama was a Christian. These gaffes are ephemeral, and insofar as they ought to inspire concern among his supporters, it's mostly about clumsy handling of fairly straightforward questions.

Yet the ISIS answer reveals one of Walker's biggest weaknesses: foreign policy. Marco Rubio can point to his experience on the Senate Foreign Relations Committee. Jeb Bush has tried to move quickly to articulate a theory of foreign relations—partly in response to comparisons to his brother George W. Bush. While he hasn't gotten very far with that, he benefits among hawks from his association with the Bush family (and, needless to say, suffers from it among conservative doves and moderate swing voters). Rand Paul and Ted Cruz can't claim extensive foreign-policy experience, but they profit from having strongly articulated ideological approaches. Not so with Walker.

The backlash to Walker's comment echoes, in a peculiar way, some of the circa-2007 derision of Senator Barack Obama as nothing more than a community organizer without the chops to handle the world. (Perhaps Walker, by virtue of his anti-union offensive, could market himself as a community disorganizer?) Like Walker, who caused a ruckus when he decided to "punt" on a question about evolution in London, Obama's foreign trips didn't always go smoothly.

In the end, it didn't matter to voters. In fact, the political class may consistently make unrealistic demands for foreign-policy experience in presidential candidates—many of whom come from governor's mansions—whereas having extensive foreign-policy experience is arguably politically overrated. Among recent presidents, none had a longer global resume than George H.W. Bush, a former CIA director, ambassador to the United Nations, and de facto ambassador to China. Bush defeated a feckless Michael Dukakis in 1988 but couldn't win reelection against Arkansas Governor Bill Clinton in 1992.

The obvious rebuttal: What about the policy, stupid? And here, opinions will diverge based on what you think about Obama's foreign policy. How much, though, are the successes and limitations of Obama's foreign policy a result of his limited experience before taking office? My colleague Conor Friedersdorf has argued repeatedly that having won the 2008 Democratic primary by accurately painting Hillary Clinton as a hawk who badly misjudged the war in Iraq, Obama surrounded himself with hawks and Clinton confidantes who had made the same errors (most notably Clinton herself, as secretary of state).