Foreign policy hasn’t played much of a role in the Republican presidential race, and it’s easy to see why.

GOP candidates’ remarks on our role abroad have ranged from the uninformed to the bizarre (with the exception of Jon Huntsman, who served twice as a U.S. ambassador). Front-runner Mitt Romney’s foreign-policy speech last week had a Rip Van Winkle quality to it, as though he’d just awakened after a decade and was unaware of how the world had changed since 9/11.

This is sad, because the country could use a serious national debate over what our global role should be in a time of economic turmoil and scarcity. But Republicans seem far more interested in hammering President Obama’s “weakness” abroad than addressing the real threats to our global standing. Romney may insist that “the 21st century must be an American century,” but repeating that mantra won’t make it so.

Yet Republican wannabes have set forth no realistic roadmap for how America can maintain its role as global leader. Most have stumbled badly when asked foreign-policy questions. Texas Gov. Rick Perry confused India and Pakistan. Former Sen. Rick Santorum opined that we deal with Pakistan by cozying up to ousted Pakistani dictator Pervez Musharraf — who is now in exile in London and faces arrest if he returns home.

Former pizza king Herman Cain made light of his foreign-policy ignorance with a joke: “When they ask me who is the president of Ubeki-beki-beki-beki-stan-stan, I’m going to say … I don’t know.” I won’t even start to track Michele Bachmann’s jumbled foreign-policy claims.

Which brings me back to Romney, whose positions reflect the fact that he’s hired on a host of former George W. Bush advisers. He talks of restoring American strength by adding 100,000 U.S. troops and expanding defense spending. Yet he never mentions our budget crisis, although both parties have agreed defense cuts will be required to address it. He never explains how we can afford 100,000 additional soldiers when we’re overburdened with debt.

Nor does he address what kind of strategic force we need to confront the threats of the future, which should determine the size of our forces. We’re unlikely to repeat the kind of ground wars we’ve waged in Afghanistan and Iraq, while drones and special forces are most effective for tracking down terrorists.

Did Romney avoid these issues because he didn’t want to cite Obama’s success in sending special forces to kill Osama bin Laden? Perhaps. But it’s bizarre to pledge a vast increase in military manpower when you don’t say why it is needed.

This lack of seriousness runs through every aspect of Romney’s foreign-policy posture. On Afghanistan, he’s backed off from an earlier pledge to bring troops home soon and now talks of a “full review” of our policy. Do we really have time for — or need — yet another full review? On the Middle East, he ignores failed peace talks but promises to focus aid and diplomatic efforts, even as Republicans slash the State Department budget.

And on Iran, Romney talks tough — saying an Iran with nukes is “unacceptable” — but he doesn’t say how he’d act differently than Obama. Perhaps that’s merciful, because other Republicans (including the normally level-headed Huntsman) are talking of military strikes against Tehran.

Never mind that most serious Iran experts believe a strike would not eliminate Tehran’s nuclear program, but would have huge, negative repercussions. (We should keep this warning in mind as hysteria rises over an alleged Iranian plot to kill the Saudi ambassador to Washington, an allegation that Iran experts find bizarre and contrary to Tehran’s operational style.)

This, in the end, is what disturbs me most about Republican foreign-policy posturing: The GOP seems unable to grasp that the world has changed and that the United States must adapt.

Huntsman does get it. He rightly labels the need to “rebuild America’s core” as America’s No. 1 national security issue: Joblessness (not to mention failing infrastructure and education) undercuts America’s ability to lead.

And he understands the need to “right-size our current foreign entanglements,” including a gradual drawdown from Afghanistan, and more focus on intelligence gathering and special forces to fight terrorists.

In fact, if you read Huntsman’s speech, it doesn’t sound so different from where Obama has arrived through trial and error. I’ve had big gripes with Obama’s foreign policies, but at least he’s trying to grapple with the requirements of new times.

However, Huntsman won’t get the nomination. So we’re left with a GOP pack that insists on American superiority and sabre-rattling while our country is crumbling internally. From such self-delusion, the next American century won’t grow.