Then he made an iron vow to get American troops out of Iraq within 16 months. Neither Obama nor anyone else has any clue what the conditions will be like when the next president takes office. He could have responsibly said that he aims to bring the troops home but will make a judgment at the time. Instead, he rigidly locked himself into a policy that will not be fully implemented for another three years.  If Obama is elected, he will either go back on this pledge — in which case he would destroy his credibility — or he will risk genocide in the region and a viciously polarizing political war at home.  Then there are the cultural issues. Charles Gibson and George Stephanopoulos of ABC News are taking a lot of heat for spending so much time asking about Jeremiah Wright and the “bitter” comments. But the fact is that voters want a president who basically shares their values and life experiences. Fairly or not, they look at symbols like Michael Dukakis in a tank, John Kerry’s windsurfing or John Edwards’s haircut as clues about shared values.  When Obama began this ride, he seemed like a transcendent figure who could understand a wide variety of life experiences. But over the past months, things have happened that make him seem more like my old neighbors in Hyde Park in Chicago.  Some of us love Hyde Park for its diversity and quirkiness, as there are those who love Cambridge and Berkeley. But it is among the more academic and liberal places around. When Obama goes to a church infused with James Cone-style liberation theology, when he makes ill-informed comments about working-class voters, when he bowls a 37 for crying out loud, voters are going to wonder if he’s one of them. Obama has to address those doubts, and he has done so poorly up to now.  It was inevitable that the period of “Yes We Can!” deification would come to an end. It was not inevitable that Obama would now look so vulnerable. He’ll win the nomination, but in a matchup against John McCain, he is behind in Florida, Missouri and Ohio, and merely tied in must-win states like Michigan, Minnesota, New Jersey and Pennsylvania. A generic Democrat now beats a generic Republican by 13 points, but Obama is trailing his own party. One in five Democrats say they would vote for McCain over Obama.  General election voters are different from primary voters. Among them, Obama is lagging among seniors and men. Instead of winning over white high school-educated voters who are tired of Bush and conventional politics, he does worse than previous nominees. John Judis and Ruy Teixeira have estimated a Democrat has to win 45 percent of such voters to take the White House. I’ve asked several of the most skillful Democratic politicians over the past few weeks, and they all think that’s going to be hard.  A few months ago, Obama was riding his talents. Clinton has ground him down, and we are now facing an interesting phenomenon. Republicans have long assumed they would lose because of the economy and the sad state of their party. Now, Democrats are deeply worried their nominee will lose in November.  Welcome to 2008. Everybody’s miserable.  A version of this op-ed appears in print on , on Page A25 of the New York edition with the headline: How Obama Fell To Earth. Today's Paper|Subscribe
Furiously courting Democratic primary voters and apparently exhausted, Barack Obama has emerged as a more conventional politician and a more orthodox liberal.