News reports published in the last week have stated that the Obama campaign will make a primary theme of the Democratic National Convention the argument that a victory for John McCain will merely represent an extension of the unpopular George W. Bush presidency.

On one hand, this possibility accentuates the drag that Bush represents on the Republican ticket. Media commentators have focused their attention on the question of why McCain is so close to Obama in the polls despite all of the generic signs of a bad Republican year; another way to look at the same question is to ask where Obama, with thinner credentials than any major party nominee since Wendell Willkie, would be if Bush’s approval rating was 55 percent instead of 35 percent. The probable answer tells us how central Bush’s difficulties are to Obama’s hopes.

On the other hand, a decision to turn the Democratic convention into an unrelenting hunt for the Bush-McCain monster may prove to be a poor use of the convention.

For one thing, Obama has been trying with great regularity for the last several months to make the Bush-McCain connection stick, but with only limited success. Politically aware Americans know that McCain and Bush have been at odds on a number of important issues since their titanic nomination battle in 2000. McCain is not Bush’s vice president, and it will be much harder to pin real and perceived presidential shortcomings on him the way that Richard Nixon pinned them on Hubert Humphrey, Ronald Reagan on Walter Mondale, or George W. Bush on Al Gore.

McCain himself has a number of good defenses against the charge, which he will undoubtedly deploy (though perhaps delicately) throughout his own convention. And because the Republican convention follows hard on the heels of the Democratic convention, McCain will get the last word on the subject, perhaps before the Democratic argument has even had a chance to sink in. Obama will have given his best shot, but in the end it is very possible that not much will have changed in the race.

The danger is that the opportunity cost for Obama if he takes this course could be high. Though McCain has run a much improved campaign in recent weeks and showed himself to be a formidable opponent at the Saddleback Civic Forum, Obama’s biggest obstacle isn’t McCain, it is himself. His thin record of accomplishment and short time in public life mean that he must use his convention, above all, to help American voters reach a level of comfort that they have not yet attained with him as a person and as a political figure.

Obama remains, in the minds of many Americans, a big question mark. His policy pronouncements are vague, his associations are questionable, his record in the U.S. Senate and the Illinois legislature is minimal, his enthusiastic embrace by foreign crowds not normally disposed to wish the United States well is troubling. His frequent shifting around since early June has only served to raise more questions.

The Democratic convention may be Obama’s last big chance to try to answer those questions on his own terms. On some counts, the task may be beyond him (how does one explain away Bill Ayers?), but on others, the convention offers him a venue well-designed for the exposition of biography and policy.

Using it instead primarily as a bludgeon to establish a largely spurious connection between Bush and McCain could work, but just as likely will not. There are many more holes in the public’s knowledge of Obama’s story than in its knowledge of McCain’s. If Obama doesn’t use his convention effectively to fill them in first, the Republican convention a week later surely will. Then the Bush-McCain monster will sink out of sight, replaced by the ubiquitous McGovern-Obama creature, which may prove more enduring because it is more plausible.

Andrew E. Busch is a Professor of Government at Claremont McKenna College and an Adjunct Fellow of the Ashbrook Center.