Americans have not had a serious presidential debate over foreign policy since at least 1980, when Jimmy Carter and Ronald Reagan offered two distinctly different views of the Soviet threat. That was a generation ago. With the end of the cold war, foreign affairs simply disappeared from the political landscape, becoming a niche issue for the Council on Foreign Relations set.

Of course the world didn’t go away, as we learned brutally on September 11, 2001. In fact, the years after the end of the cold war have begun to erase the distinction between home and abroad. When Russia had a banking crisis, it turned into a global panic. When China had public-health problems, SARS spread across the region. When Arab regimes have failed to modernize, we’ve all had to deal with terrorism. And during these years, America has become the world’s sole superpower. So at a time when the globe was becoming smaller, when America came to occupy a historic position, when its actions were having a massive effect across the world, its leaders stopped talking to the public about foreign affairs. As a result, the American people have never had the conversation they deserve about America’s role in this new world.

Foreign policy has made the occasional cameo appearance during campaigns. But without a sustained discussion, all that anyone remembers is sound bites and attitudes. In the last campaign the little tidbits we heard–Bush said he was against nation-building and in favor of humility–turned out to be deeply misleading. In retrospect, it would have been worth having had those thoughts fleshed out some. This time we could do better, and not simply through stump speeches. Why not take one of the three scheduled presidential debates and devote it entirely to foreign policy? (It’s been done in the past.) After all, we’re living in an age of terrorism, we have 140,000 American troops in Iraq and Afghanistan, are spending tens of billions of dollars on homeland security and are implementing new policies to deal with weapons proliferation and terror worldwide. Shouldn’t we discuss all this?

In a sense George W. Bush has begun this process. Over the last three years, and especially since 9/11, President Bush has outlined a distinctive, even coherent, foreign policy. He has explained which general principles he would be guided by when addressing new threats, which instruments of foreign policy he values, what weight he places on alliances and international institutions, and so on. John Kerry has the perfect opportunity to explain his own contrasting set of principles for America’s involvement with the world.

The challenge for Kerry is to steer clear of two temptations. The first is to have a foreign policy that is simply anti-Bush. Let’s call this the Howard Dean position, in substance but also in tone; if Bush is in favor of something, it must be wrong. But while anti-Bush works well in the Democratic primaries, it is too reactive and negative for the general election. It’s also bad foreign policy. Some of George Bush’s policies, after all, might be worth embracing. Pure anti-Bushism also sends a signal to some Americans that the Democratic Party is driven crazy by a warrior president, and that it is a party that remains uneasy about the use of military force.

The second temptation, far less tempting these days, is to be Bush-lite. Let’s call this the Joe Lieberman position. It’s wrong for two reasons. First, whenever voters have to choose between two such offerings, they will always go for the real thing. Second and more important, Bush’s foreign policy is serious and coherent. But it is also quite radical, breaking with decades of previous policy in key areas. A Democrat must point this out and present an alternative to it.

That’s the challenge for Kerry: to be something other than merely anti-Bush or Bush-lite. He will have to talk about how he would address the new threats America faces, but also what his vision is for America’s place in the world. The good news is that after decades, the public may finally be listening.