The weakest part of our political system is the presidential nomination process. And it's not coincidental that it's the part of the federal system that finds least guidance in the Constitution.

There is no provision in the Constitution that says that Iowa and New Hampshire vote first. The idea of giving any two states a preferred position in the process of choosing a president would surely have struck the Framers as unfair.

But we are stuck with Iowa and New Hampshire voting first because no politician who contemplates ever running for president -- i.e., most politicians -- wants to arouse the ire of the political and journalistic establishments of Des Moines and Manchester.

Another feature of the nominating system is that it tends to exclude those with experience in foreign and military policy, the two areas in which presidents tend to have the greatest leeway.

Dwight Eisenhower did have such experience. And Richard Nixon, Lyndon Johnson, Gerald Ford and George H.W. Bush had been vice presidents with varying degrees of involvement in foreign policy and military command.

But the other seven presidents of the last 60 years had to learn by doing. And Ford's ascent came not through the nomination process but through the 25th Amendment.

A third problem is that the lengthiness of the nomination process -- the permanent campaign, as Sidney Blumenthal dubbed it long ago -- means that a president, and the nation, may be stuck with an agenda set as much as 10 years before he leaves office.

And that's in the best case, when a candidate presents a series of policy initiatives to caucus-goers, primary voters and the general electorate, and then tries to follow through in office, as George W. Bush and Barack Obama can claim to have done.

In the worst case, a candidate briefly captures the imagination of impressionable activists and voters with personal glamour and vaporous rhetoric, and then edges ahead of his rivals to clinch a nomination in a good year for his party.

That's what some people think happened in 1976 with Jimmy Carter, though I think that's unduly harsh. Certainly it's a fair characterization of what might well have happened in 2008 if John Edwards had gotten a few more votes and come out ahead of Barack Obama as well as Hillary Clinton in the Iowa caucuses.