|US president, Barack Obama [Photo:BBC]|
He highlighted the differences between his aims and Republican policies, and reprised his 2008 theme of "hope".
"I never said this journey would be easy, and I won't promise that now," Mr Obama told the Democratic convention.
Mr Obama told delegates in the hall and voters watching at home that the nations problems have built up over "decades" and cannot be fixed in a flash.
"But when you pick up that ballot to vote - you will face the clearest choice of any time in a generation.
"Over the next few years, big decisions will be made in Washington: on jobs and the economy; taxes and deficits; energy and education; war and peace - decisions that will have a huge impact on our lives and our children's lives for decades to come," he said.
Mr Obama took the stage not in a huge stadium in downtown Charlotte, North Carolina, as organisers had hoped, but inside the convention centre after Thursday's speech was moved because of weather concerns.
He followed a rousing speech by Vice-President Joe Biden, who praised Mr Obama for his bravery in bailing our the auto industry and ordering the killing of Osama Bin Laden.
The president offered a string of critiques of Republican policies, describing his opponents as "happy to talk about everything they think is wrong with America" without offering suggestions on how to make things right.
"That's because all they have to offer is the same prescription they've had for the last thirty years," he said.