The lack of incumbents on the ballot, the War in Iraq, the front-loaded schedule, and the unusual mix of backgrounds among the candidates make this cycle's primaries and general election subject to change without notice, Bill Kristol opines in Time:

Lesson: the improbable sometimes happens. And what's true in sports is true in politics. There hasn't been a major upset in a presidential-nomination race since Jimmy Carter's victory in 1976. We're due. And the 2008 presidential campaign is an especially good candidate to provide a surprise. Why?

1. It's an open-seat election. For the first time since 1952, there will be no incumbent President or Vice President on the ballot. As we know from state and local elections, nonincumbent races are more volatile and less predictable than those with incumbents, which tend to be reasonably predictable referendums on the party in power. But in 2008 there won't be an incumbent, and there won't even be someone who resembles an incumbent: none of the leading Republicans have worked in or been particularly close to the Bush Administration. Indeed, the three leading Republicans and two leading Democrats have never run for national office before. Much more depends in such circumstances on unpredictable factors like candidates' errors, campaign dynamics and external events than in a traditional incumbent contest.

2. It's a wartime election. Wars are volatile. Eight months ago, we were losing in Iraq. Now it's not so clear. Where will Iraq stand four months from now, at the time of the Iowa caucuses--or 14 months from now, in November 2008? As wars are unpredictable, so are the politics of war.

Read the whole column at the link above. One minor correction: it's the first time since 1928 no incumbent President or Vice President has been on either party's ballot. While there was no incumbent in the general election of 1952, Truman was a candidate for reelection until losing the New Hampshire primary (then held in March . . . ah, the good ol' days!) to Senator Kefauver and withdrawing from the race.

Surprises are certainly in store, but they are hardly unique to this year.

Events have suddenly doomed or launched many a candidacy over the years (mostly doomed, though). Recall George Romney's "I was brainwashed" remark killed his chances in 1968, while LBJ got out after winning the New Hampshire primary with only a plurality. Ed Muskie was a shoo-in in 1972 until he broke down in tears on the street in Manchester, NH, after the Union Leader questioned his wife's finances. In 1980, after losing Iowa, Reagan reasserted his status with "I paid for this microphone!"

In 1988, frontrunner Gary Hart dared reporters asking about rumored affairs to "Follow me." They did, he did, he was out, in again, and out again. Eventual nominee Dukakis blew whatever chance he may have had by looking ridiculous riding in a tank and muffing a debate question on "What if your wife was raped and murdered?" Bill Clinton bolstered his chances by blasting Sista Souljah in 1992. Howard Dean was riding high in 2003 before he declared the capture of Saddam Hussein "doesn't make us safer," and then acted like a fool in the last debate before the Iowa caucuses. His famous scream was the final nail in his political coffin.

So, surprises are more the rule than the exception in presidential campaigns. This one promises to be filled with them. Stay tuned.