The Democrats did what everyone knew they had to do: nominate Barack Obama by acclamation on the first ballot of their convention in Denver. But Hillary Clinton made everyone wait until nearly halfway through the balloting before making that inevitable motion, and in so doing underlined the chief lesson of the convention. The delegates were almost evenly split between her and Obama, and the deep division in the party was painfully evident.

The reservation so many delegates had about Obama had one clear cause, and it had nothing to do with the fact that he is black. On the contrary, the fact that he is an African-American counted heavily in his favor, and may have been the decisive factor in his victory. The reservation has to do with his lack of experience. Obama became an attorney, served as a member of the Illinois State Senate for eight years, and was then elected to the U.S. Senate in 2004. He has served in that capacity for fewer than four years -- his only experience in a federal office. And now, as intractable problems beset the U.S. economy and the Middle East is wracked by turmoil, he offers himself as a candidate for the presidency of the United States.

One doesn't have to be an excessively partisan Republican, or indeed a Republican at all, to wonder whether a man with a record that anemic is ready to shoulder the somber burdens of the presidency. How broad and deep is his understanding of the American economy -- or indeed, of economic principles in general? Even more important, perhaps, is how ready is such a man to take on the leadership of the world's most powerful nation in its dealings with other countries?

These are fair questions, and they worry a great many people who are far from being Republicans. John McCain, the likely Republican nominee, has 22 years' experience in the U.S. Senate, serving on the Judiciary Committee and the Foreign Relations Committee. No one can gainsay the expertise he has acquired in these capacities.

Despite the wide disparity in these two records, Obama is probably the front-runner in their looming contest. According to the conventional wisdom, 2008 should be a "Democratic year." The Republicans have controlled the White House for the past eight years, and Congress for six of those eight. In a two-party political system like ours, it is more or less "time" for the GOP to step aside and give the Democrats a chance. Nor has the Republican record been all that stellar. The Iraq war (though now going better at last) is far from popular, and public apprehensions about the economy are all too obvious. Conventional wisdom tells us that, in such a situation, it's "time for a change."

But this is precisely why Obama's spectacular lack of any serious preparation for the presidency looms so large in the public's mind. If we throw the Republicans out, exactly whom are we throwing in? What does Obama know about the likely consequences of a tax cut -- or a tax hike? How fast, in the next four years, can he learn the tricky business of dealing with enemies like Iran's President Mahmoud Ahmadinejad, or even such "friends" as the rulers of Saudi Arabia? Will he know, or sense, when to pull back in his dealings with foreign powers and when to apply pressure?

No doubt, despite assertions to the contrary, there is always an element of "on-the-job training" in serving as president, but what in Obama's background, in the hardscrabble politics of Southside Chicago, equips him to be a fast learner in this highly specialized field? Presumably he will be surrounded by knowledgeable advisers, but every president has testified to the difficulties presented by their often-conflicting advice.

So the doubts inspired in many voters by Obama's record, or rather his spectacular lack of one, are thoroughly justified. And, despite all the factors that make 2008 a year of likely victory for the Democratic Party, those doubts are a formidable obstacle to his candidacy for the presidency of the United States.