After all, he had less experience in office than many of his rivals. He was not as well-known. He had the potential electoral liability of being black. No one knew if he was tough enough to stand up to Republican assaults in a nasty campaign.
So what accounts for his success? More than any other reason, he won because he had opposed the invasion of Iraq -- which Clinton and others had endorsed. Obama was the peace candidate of 2008. As the long and costly war dragged on, that was a priceless asset.
Where are those voters now? The majority is probably still in Obama's camp. Most Democrats in Congress have defended the president's attack on Libya. Most have given him the benefit of the doubt in his slow withdrawal from Iraq. Most have gone along with his dramatic escalation in Afghanistan.
But the mood of Democrats may be changing. The liberal magazine The Nation decried the intervention in Libya as "flagrant hypocrisy." John Larson, chairman of the House Democratic Caucus, upbraided Obama for not consulting Congress.
Rep. Dennis Kucinich, D-Ohio, called the war "another disaster." If our involvement lasts weeks or months instead of days, Obama could lose many Democratic members.
He has already lost a lot of them on Afghanistan. Recently, 85 House Democrats voted for Kucinich's resolution demanding withdrawal of U.S. forces by Dec. 31, with 99 voting no. Sen. Sherrod Brown, D-Ohio, says both he and "a lot of my colleagues" in the Senate will also push for a speedy and complete departure.
Obama has promised to withdraw some troops beginning in July, but he is committed to staying around till 2014. An unnamed senior official told ABC News this month "a substantial reduction is now 'unlikely.'" Barring unexpectedly quick gains in security, most of our troops will still be there when the Iowa caucuses are held.
The combination of Afghanistan and Libya could bring a bitter end to the romance between Democratic liberals and Obama. Many of them were already disappointed with him for extending the Bush tax cuts, bailing out Wall Street, omitting a public option from the health care overhaul, offering to freeze domestic discretionary spending and generally declining to go after Republicans hammer and tong.
Had he rejected demands to use military force against Moammar Gadhafi, they would have had the solace of seeing the hawks finally put in their place. Instead, Obama did in Libya about what Clinton or John McCain probably would have done.