Those two items will shape the race and make it different from other presidential elections of recent times. Voters will look for candidates who can show an ability to fight terrorism, keep the country safe and show competency in foreign policy. Oh, traditional domestic issues — jobs, health care and education — will still be there, but they'll now have to share the stage with these fresh concerns.

In 2000, terrorism and foreign policy weren't big factors in the race between Al Gore and George W. Bush. Today, former New York Mayor Rudy Giuliani leads in early polls because of the success he had managing the aftermath of the attack on the World Trade Center. You could see the shift begin in 2004, when Bush narrowly defeated John Kerry, largely because more Americans saw Bush as better able to defend the country.

But in 2008, the race will be wide open. Which candidates could be helped by this shift in issues? In addition to Giuliani, some of the often-maligned "Washington candidates" may profit because their experience may now be worth more to voters who are looking for someone competent to protect the nation. (I've never quite understood the logic that says we should elect someone president largely because they're from "outside" Washington. That's a bit like picking a chairman of GE who doesn't care for electricity.)

On the Republican side, Arizona Sen. John McCain, who earned his credibility on defense questions in a North Vietnamese prison, could benefit. That said, both Giuliani and McCain would have to get past their party's religious conservatives to win the GOP nomination.

On the Democratic side, retired Gen. Wesley Clark, a former NATO commander, has spent an adult lifetime dealing with security questions. Indiana Sen. Evan Bayh, who combines experience in a governorship with service on the Senate armed services and intelligence committees, could gain. These are centrist Democrats who might be formidable contenders, if they can get past the angry left of their party.

There is much upside potential in a Bayh candidacy in Iowa. For openers, he's a Midwesterner. That gives him a regional advantage. Look at some people who've done well in caucuses — George McGovern of South Dakota, 1972; Walter Mondale, Minnesota, 1984; Dick Gephardt, Missouri, 1988; Bob Dole, Kansas, 1988 and 1996.

And Bayh must understand how to win in rural America, since he's carried statewide elections for secretary of state, governor and U.S. senator in a Republican state. He's also low-key, somber and slightly stiff. Just like a lot of Midwesterners.

There's another pattern you notice in looking at 30 years of caucus winners and losers: The most extreme candidates often don't win. Despite all the media attention they get, when rank-and-file party members show up on caucus night, they tend to pick candidates more in the middle of that year's political spectrum.

And who might be hurt by this changed emphasis in issues? Governors. They've done well in recent presidential cycles but could now be disadvantaged if they can show no particular competency on foreign policy or defense questions. That hurts potential candidates such as Iowa Gov. Tom Vilsack, a Democrat, or Arkansas Gov. Mike Huckabee, a Republican. New Mexico's Bill Richardson may avoid the problem because he's had national experience in both diplomatic and energy issues.

This security factor will be particularly acute for Democrats. Polls show voters often see Republicans as more qualified to handle issues of national defense and terrorism. For Democrats to win the White House in 2008, they must nominate a candidate who above all is seen by voters as someone who will keep them safe.