2012 Democratic National Convention in Charlotte, N.C.

CHARLOTTE, N.C. — Four years after riding a wave of optimism into the White House, President Obama offered a sobering message as he asked Americans for another term to help complete the country’s recovery from the worst economic crisis since the Depression.

Accepting the 2012 Democratic nomination Thursday night, Obama offered an updated version of the message of hope and change that brought him to office. He said that he’d been humbled by the burdens of office and told millions watching on TV that he feels the sorrows of ordinary Americans who have lost loved ones in war or their homes or jobs to the recession.

“While I’m very proud of what we’ve achieved together, I’m far more mindful of my own failings, knowing exactly what Lincoln meant when he said, ‘I have been driven to my knees many times by the overwhelming conviction that I had no place else to go,’” the president said near the end of his 38-minute speech.

Pledging “promise and prosperity” in the next four years, Vice President Joe Biden served as a warm-up act  on the final night of the Democratic National Convention. Caroline Kennedy and former Rep. Gabrielle Giffords of Arizona were among the speakers.

Obama’s address was moved indoors due to threats of thunderstorms, disappointing tens of thousands of ticket holders. “We can’t let a little thunder and lightning get us down. We have to roll with it,” said the president in a conference call. “All I can tell you is how much I appreciate everything you’ve done.”

Archive photos: 1960 Democratic National Convention in Los Angeles

MORE: Michelle Obama, Julian Castro highlight DNC opening night