Barack Obama surprised even some seasoned political observers when he coupled the announcement that he had formed an exploratory 2008 presidential campaign committee with the news that he is all but certain to formally enter the race for the Democratic nomination on February 10. But there was nothing surprising about the message he presented. It was more of the same vaguely satisfying criticism of “the smallness of our politics” and the way government is “gummed up by money and influence,” along with flowery promises to “tackle the big problems that demand solutions” and help us “come together around our common interests and concerns as Americans.”

To his credit, Obama recognized in his announcement many of the challenges that face the United States: skyrocketing healthcare bills, lost pensions, the high price of a college education, the need to break our dependence on foreign oil and, above all, the fact that “we’re still mired in a tragic and costly war that should have never been waged.” But, as has been the case since speculation heated up about a run by the freshman senator from Illinois, Obama was long on personal appeal and short on policy specifics.

The seriousness with which he approaches the task of defining his politics between now and February 10 will go a long way toward deciding whether Obama wins his party’s nomination. If he’s going to secure the critical support of grassroots Democrats in key early caucus and primary states, these coming weeks must be less about celebrity and more about policy.

To be sure, Obama is a superstar, which allows him to leap over many of the hurdles erected by the overseers of the political process. Even before his keynote address at the 2004 Democratic National Convention, he was the most prominent state legislator in the nation. After his speech, favorably received by delegates and by most of the political and media class, he secured his Senate seat and arrived in Washington accompanied by some of the highest expectations ever attached to a new member of Congress.

Predictably, Obama failed to meet those inflated expectations. His relative caution on the big-picture issues of Iraq and domestic civil liberties, combined with some disappointing votes on consumer and economic issues, alienated many activists. As Obama made the rounds of state party conventions, fundraising events and rallies during the 2006 Congressional election season, however, grassroots Democrats remembered his inspired convention speech rather than his uninspired votes in Washington. And they gave the Senate’s only black member a welcome that most politicians can only dream of. The message from the party faithful was clear: New York Senator Hillary Clinton, the presumed frontrunner, had not closed the deal. There was an opening for another first-tier contender in the race, and Obama could take it.

Can Obama catch up with Clinton and former North Carolina Senator John Edwards, both of whom are far ahead in putting together the multistate campaign apparatus needed for a fast-paced presidential campaign? Yes, but only if the grassroots Democrats who have been so enthusiastic about the prospect of his candidacy now turn that enthusiasm into practical commitments in states like Iowa (where the first caucuses will be held a year from now) Nevada, New Hampshire and South Carolina. That transition will have something to do with Obama’s star power, of course, but it will have much more to do with the intensity and effectiveness of his calls for ending the war in Iraq, restoring civil liberties protections at home and undoing the Bush Administration’s misguided economic policies.

As he attempts that task, there will be a good deal of media discussion about how Obama must compete with Clinton, but that’s not the right test. If she runs, Clinton will do so as what she is: a cautious centrist with lots of money and prominent support but with dubious appeal to the activists who define the early stages of the nomination process. Obama’s more serious challenge will be to make sure he compares favorably with Edwards. The 2004 Democratic nominee for Vice President has done a good job of identifying himself as the Democrat who wants to bring the troops home from Iraq–most recently in a speech at New York’s Riverside Church, where he recalled the antiwar rhetoric of the Rev. Martin Luther King Jr. and called for Congressional Democrats to refuse to fund the Iraq “surge.” On the home front Edwards has advocated tax fairness, universal healthcare and living-wage protections. And he has spent a lot of time talking about those issues with activists with the power to make or break candidates. Edwards is attracting endorsements–particularly from labor union leaders and members–and the volunteer support that is required in high-maintenance states like Iowa and Nevada.

There’s no question that Democrats like Barack Obama. But they don’t necessarily know why. If Obama can fill in the blanks, he could trump Clinton and Edwards. If he can’t, he’ll likely join the long list of Presidents who might have been.