A reasonably evenhanded biography of Barack Obama, published last year, describes him as "an exceptionally gifted politician who, throughout his life, has been able to make people of wildly divergent vantage points see in him exactly what they want to see." The biographer, David Mendell, reports, "the higher he soared, the more this politician spoke in well-worn platitudes and the more he offered warm, feel-good sentiments lacking a precise framework."

    Now, less than four months before Election Day, with growing disquiet among significant portions of Obama's progressive base, the current negative reactions can't be dismissed as potshots from the political margins. Even The New York Times, in a July 4 editorial headlined "New and Not Improved," has expressed alarm: "We are not shocked when a candidate moves to the center for the general election. But Mr. Obama's shifts are striking because he was the candidate who proposed to change the face of politics, the man of passionate convictions who did not play old political games."

    But on July 8, Obama made a valid point - even if it wasn't exactly the point he was trying to make - when he disputed "this whole notion that I am shifting to the center" and argued: "The people who say this apparently haven't been listening to me." Overall, his career as a politician has embraced conciliation and compromise rather than pushing against centrist corporate agendas.

    These days, an appreciable number of Obama supporters are starting to use words like "disillusionment." But that's a consequence of projecting their political outlooks onto the candidate in the first place.

    The best way to avoid becoming disillusioned is to not have illusions in the first place.

    The more that spotlights move from Obama's uplifting eloquence to his specific policy positions, complete with loopholes and wiggle room, it's predictable that some of his progressive base will become displeased - whether on issues related to the death penalty, fair trade, government funding of religious-based projects, Iraq, Iran, evenhandedness between Israel and Palestinians, gun control or (perhaps most flagrantly) warrantless surveillance.

    On Wednesday, when Obama cast a vote in the Senate to undermine the Fourth Amendment, he fulfilled his frequent prediction during the primary season that "I will make mistakes." This was a very big one. As an attorney who's well acquainted with constitutional law, he participated in damaging one of the most precious provisions in the precious Bill of Rights.

    Barack Obama is an extremely smart guy. And I can't remember a major contender for president less inclined to insult the intelligence of the public. Let's return the favor by directly challenging him when appropriate. We'd do him - and the Obama campaign, ourselves and the country as a whole - no favors by opting for silence instead.

    We can help the Obama for President effort when we hold him to his good positions - and move to buck him up when he wavers.

    While speaking of the Iraq war, Obama made one of the most insightful statements of the primary campaign: "I don't want to just end the war; I want to end the mindset that got us into war." He needs to be held to that wisdom. Obama should feel enormous counterpressure from the grassroots against the forces in the media and foreign-policy establishment that are pushing him to go wobbly on ending the Iraq war.

    The vortex of what Martin Luther King Jr. called "the madness of militarism" is enormously powerful - and, in the context of presidential politics, routinely enticing. To the extent that Obama gears up anti-Iran rhetoric that he seemed to have mercifully abandoned months ago, for instance, he may reassure some pundits and other influential power brokers in Washington, but at the same time he's liable to weaken some of the allegiance to his candidacy among progressive constituencies.

    As an elected Obama delegate to the Democratic National Convention, I've been hearing from people who are upset by the recent direction of the campaign. Some were always a bit skeptical of Obama, but are becoming much more so. Others have been strong supporters from the outset. In the latter category, an attorney sent an email to me a few days ago: "I must confess that my enthusiasm for Senator Obama has waned in recent weeks with a number of his policy announcements (on FISA, gun control, etc.). While I of course will vote for him and help him get elected, I must say that I feel a bit deflated after having put so much hope, effort and money into his candidacy."

    Obama and his top advisers will have to gauge the importance of such deflation and waning enthusiasm. A key factor in the election will be the extent to which the Obama campaign can pull off a massive mobilization of voters. Deflated constituencies don't mobilize as well as inspired ones.

    Anyone who assumes Obama will be elected president in November is on ground as solid as the assumption in 2000 that Al Gore would be elected president. On July 9, when releasing new results from nationwide polling, the Democratic research outfit, Greenberg Quinlan Rosner, reported Obama has a mere four-point lead over John McCain. Despite its propensity to spin for Democrats and its eagerness to note Obama seems "well-positioned," the firm acknowledged "some diminished enthusiasm for the presumptive Democratic nominee and only small gains among independent voters."

    Some progressives, now disaffected, might consider the prospect of Obama falling short on Election Day to be his problem, not ours. But this isn't about Obama. It's about whether the levers of power in the Executive Branch, and the Supreme Court along with it, are going to be redelivered into the hands of the right wing for yet another four years.

    We're facing the historic imperative of keeping McCain out of the White House. If major progressive change is going to be feasible during the next several years, defeating McCain in November is necessary. And insufficient. The insufficiency does not negate the necessity.

    Under a McCain presidency, we'd be back to square one, where we've found ourselves since January 2001. Putting Obama in the White House would not by any means ensure progressive change, but under his presidency, the grassroots would have an opportunity to create it.

    Along the way, let's strive to eliminate disillusionment by dispensing with illusions. No one who is a presidential candidate can proceed to overcome corporate power or the warfare state. The pervasive and huge problems that have proved to be so destructive are deep, structural and embedded in the political economy. The changes most worth believing in are the ones social movements can make possible.