If Bush and Kerry partisans can agree on anything, it’s that the stakes tomorrow couldn’t be higher. “The most important election of our lifetime,” both parties intone. Like most pieces of conventional wisdom, this oft-repeated shibboleth leaves plenty of room for doubt.

One of the hidden strengths of the American electoral system is that it rarely presents voters with a very stark choice. Both parties hew closely to the center, and, notwithstanding pre-election bloviation, there is always a great deal of continuity between administrations. The falsity of most campaign rhetoric becomes obvious if you consider two of the most acrimonious elections of the 20th century.

In 1964,Lyndon Johnson painted Barry Goldwater as a nutty warmonger. In 1972, Richard Nixon painted George McGovern as a soft-on-communism peacenik. Yet what happened after the vote? Johnson became ever more deeply embroiled in bombing Vietnam back to the Stone Age, while Nixon went about exiting the war by cutting a deal with the communist regime in Hanoi. It’s hard to know, in retrospect, what all the fuss was about.

The choice this time is, in many respects, even less clear-cut. Both President Bush and Senator Kerry claim to be fiscal conservatives, yet each proposes a plethora of new programs to address every ill under the sun. Mr. Bush is more likely than Mr. Kerry to press for partial privatization of Social Security, while Mr. Kerry is more likely to press for partial federalization of health care. Odds are that neither man will get all he wants out of a Congress that will remain deeply divided.

There’s even less chance either candidate would make a major difference on social issues like abortion and gay marriage. Significant change will require a constitutional amendment or a radical recasting of the Supreme Court, neither of which is likely no matter who occupies the Oval Office.

What about national security policy? If you listen to Mr. Bush, the election of Mr. Kerry will result in nuclear annihilation. If you listen to Mr. Kerry, the election of Mr. Bush will result in another draft. The reality is that, no matter who’s elected, a nuclear attack could happen and a draft won’t happen.

Despite the obvious differences in style between the two candidates, they are offering pretty similar solutions to our chief foreign policy challenges. On Iraq, both promise to train local security forces, retain U.S. troops, and hold elections. On North Korea, both promise negotiations – Mr. Kerry unilaterally, Mr. Bush multilaterally. On Iran, Mr. Kerry promises to cut a deal, while Mr. Bush says he won’t; yet he gives the green light to the Europeans to deal on America’s behalf. On the Israeli-Palestinian conflict, both say they strongly back Israel while opposing Yasser Arafat. On military action, both say they’ll use force preemptively and not give the United Nations a veto on American interventions.

This is not to suggest that they’re Tweedledum and Tweedledee. Mr. Kerry is more multilateralist than Mr. Bush and less likely to use force. Yet he would face pressure from the right to prove that he’s not a peacenik, while Mr. Bush would face pressure from the left to prove he’s not a militarist. It’s possible that their actual foreign policies will be more alike than either man would care to admit.

I was reminded of this when Mr. Kerry’s adviser Richard Holbrooke called to complain about a column in which I criticized his statement that the “war on terror” is “just a metaphor.” That quote came from the New York Times Magazine, but Mr. Holbrooke tells me it was taken out of context – he’s not in the least soft on terrorism. His point, he says, was simply that we should fight individual terrorists not an abstraction like “terror.” Fair enough. Mr. Holbrooke is a hawk and I don’t have any doubt that he would prosecute the war on terror – excuse me, terrorists – pretty vigorously and skillfully. The same is true of Senator Biden, the other front-runner for secretary of state in a Kerry administration.

That hardly allays my concerns about Mr. Kerry, who has a long record as a dove and a political opportunist. But I admit he might well prove me wrong.

If he did, he would also prove wrong his more dovish supporters who think he’ll be the second coming of Howard Dean. Likewise, Mr. Bush could easily disappoint his more hawkish supporters by backing away from confrontations with North Korea, Syria, and Iran – as, in fact, he’s done during his first term.

To paraphrase Forrest Gump, the presidency is like a box of chocolates – you never know what you’re going to get. The pseudo-certainty of the campaign season will disappear as fast as the leaves of autumn.

Mr. Boot is a senior fellow at the Council on Foreign Relations and a columnist for the Los Angeles Times, where this first appeared.