We had one foreign policy debate already in the Republican presidential primary, but a great many Americans didn’t watch the 60 minutes that was on broadcast TV on a Saturday night up against a college football game. (Even fewer watched the other 30 minutes that was available only online.) So tonight will be the first time most voters see the Republican presidential candidates delve seriously into matters of war and peace, human rights, international trade and defense spending.

It is a good thing that CNN, the American Enterprise Institute and the Heritage Foundation are hosting such a debate tonight. Consider what the winner of the 2012 presidential race is likely to face: an emboldened Vladimir Putin, an Arab Spring turned frosty, a severely underfunded defense budget, a nuclear- or near-nuclear-armed Iran and a China that’s increasingly repressive at home and aggressive in Asia.

Each of the Republican contenders will need to address at least four major national security topics. In doing so they will tell us something about their preparedness to be president and their view of America’s place in the world.

The first challenge is to wrestle with the impact of the debt deal’s sequestration on defense spending. Will they reverse it? How much spending is needed? How would they defend defense? Unless the Republican president is devoted to and willing to risk political capital on upgrading and maintaining our military, most of our other national security objectives will falter. Maybe the worst misnomer of the Obama administration is that “soft power” operates in lieu of “hard power”; in fact, the potential exercise of the latter makes the former effective.

The second topic for the candidates to tackle is Iran. They will need to explain how critical it is to make sure the regime does not obtain nuclear weapons and the measures they are prepared to take to ensure that result. In sketching out how we got to where we are, what they would have done differently and analyzing how they will address our current predicament, they will tell us much about their thoughtfulness, temperament and knowledge. There is no greater security threat to the United States, and the GOP contenders better show they are up to the task of dealing with it.

The candidates will also need to define their stance on the war on terror. Do they think we must achieve victory in Afghanistan and succeed in leaving a stable, pro-Western Iraq in order to successfully wage the war against jihadist terror? Do they think the Arab Spring is an asset or a problem in combating the rise of jihadism?

And finally, the candidates would do well to explain their views on human rights. Is it a tool in our arsenal for combating totalitarian states? Is it a critical part of maintain U.S. credibility and maintaining our influence around the world? It is one thing to say that Obama has thrown human rights under the bus; it’s quite another to explain how they would treat human rights abusers in specific cases.

As for the individual candidates, the debate for many is simply an exercise in “do no harm” — or “do no more harm.” Herman Cain’s serial ignorance is probably unremediable, but he certainly doesn’t need any further gaffes. Texas Gov. Rick Perry is in single digits in the polls, but a sure way of staying there is to appear confused or reveal only a superficial understanding of foreign policy challenges.

Others should use this opportunity to show up their competitors. Rick Santorum, for example, knows a heck of a lot more about Pakistan and makes a lot more sense on foreign aid than does Newt Gingrich. Santorum shouldn’t be shy about pointing that out and challenging the race’s worst know-it-all. Likewise, Rep. Michele Bachmann (R-Minn.) sounds far more informed about everything from enhanced interrogation to Iran than Cain or Perry. And she should highlight that. These two candidates are uniquely able to lift their own profile in this debate because they know more about the topic than a number of candidates ahead of them in the polls.

For Gingrich, the challenge is to avoid sounding wacky, to show restraint and thoughtfulness and to eschew one-liners (Zero out foreign aid!). As a front-runner, he can no longer say, “That’s a complicated issue” or “This is part of a bigger discussion.” He’ll need to spell out his own foreign policy vision. And it would do him well to rein in his natural inclination to argue, badger and ridicule the moderators.

And finally for Mitt Romney, this is one more chance to impress (if that is even possible) conservatives that he really is principled and resolute on national security. He did this in his white paper and speech at the Citadel, but relatively few voters are familiar with those. If he is to begin to solidify his support, his goal should be to convince viewers that he is really the only credible candidate in the field to go up against the incumbent president and then to assume the duties of commander in chief.

The country is in bad fiscal shape these days. But there is a good argument that the world, thanks to the absence of American leadership, is in even worse condition. Voters should consider who is best suited to reverse the decline in American foreign policy effectiveness and influence. And they should consider the consequences of choosing someone who isn’t up to the task.