At 8 p.m. ET, tonight, on CNN, eight Republican presidential candidates will take the stage at D.C.'s Constitution Hall in Washington, D.C., to tell America where they stand on foreign policy and national security. It's a debate we at The Heritage Foundation are proud to co-sponsor with the American Enterprise Institute. Simply put, we did it to fill a void.

The Federal Government's responsibility to provide for the common defense is listed right in the preamble of the U.S. Constitution. That is the way we can secure the blessings of liberty. That is the subject of this evening's debate.

Important as the economy is, it's certainly not the only issue a presidential candidate must be prepared to deal with. National security is an existential concern. The President is, above all, our Commander in Chief.

Most Americans understandably focus on concerns closer to home. Will my child be able to find a job upon graduation? Will gas prices keep rising? How will I ever be able to afford retirement? Pressing as these and other domestic issues may be, a president cannot afford to concentrate solely on what's happening on the home front. One never knows what challenges will insist on barging through the White House door.

Think back to the October 2000 presidential debates between George W. Bush and Al Gore. The 9/11 attacks were less than a year away. How often did "al Qaeda" or "Osama bin Laden" came up in those debates? Not once. The word "terrorism" was uttered, in passing, in one of the debates. The word that did stand out amidst those verbal jousts: "lockbox." It went on to become the basis of a devastating skit on Saturday Night Live. But how the candidates would assure America's security, how they would respond to threats from abroad, went largely unexplored.

But crises rarely materialize out of nowhere. The signs of a gathering storm can be detected if one is paying attention.

The 9/11 attacks, for example, surprised us all, but they were hardly a bolt out of the blue. "In August 1998, Osama bin Laden's Afghanistan-based terrorist network bombed U.S. embassies in Kenya and Tanzania," Middle East expert James Phillips wrote in a paper published by The Heritage Foundation in July 2000. "Yet Afghanistan has still not received the high-level attention that it deserves as the world's leading exporter of terrorism, Islamic revolution, and opium."

We'd also seen the USS Cole bombed while it lay in port in Yemen. And let's not forget the first bombing attack on the World Trade Center in 1993.

Phillips and other experts had been sounding the alarm repeatedly by the time the 2000 election came around. Yet no debate moderator asked Gov. Bush and Vice President Gore what steps they would take, if elected, to help diffuse this threat.

It's understandable, perhaps. After all, who wants to dwell on the fact that it's dangerous out there, especially when we have enough problems at home?

But when you consider our position in the world, and what it takes to make sure that we remain secure, we see the need to be prepared -- not just in a general sense, but to anticipate specific threats and figure out how to deal with them.

At tonight's debate, the GOP candidates will have an opportunity to flesh out their views on many important defense and foreign policy challenges.

Tonight, the GOP candidates -- those who would be Commander in Chief -- will have plenty to talk about. American voters, and the world, will be listening.

Ed Feulner is president of The Heritage Foundation.