Barack Obama has formally accepted the Democratic Party's Presidential nomination in a speech to thousands of charged up party loyalists.
The president looked to recapture the energy that powered him to the White House in 2008 as he struggles with the worst poll ratings for an incumbent for 28 years.
Mr Obama was introduced by his wife, First Lady Michelle Obama, who energised the convention with her own speech two nights earlier.
He formally accepted the nomination to loud chants of "four more years" before presenting the forthcoming election as a clear choice between two competing ideologies.
He said: "On every issue, the choice you face won't be just between two candidates or two parties - it will be a choice between two different paths for America, a choice between two fundamentally different visions for the future."
In an echo of President John F Kennedy's "Ask Not" speech, Mr Obama appealed to Americans to help him to restore the country to greatness after the economic turmoil of his first term.
He said: "I won't pretend the path I'm offering is quick or easy. I never have.
"You didn't elect me to tell you what you wanted to hear. You elected me to tell you the truth.
"And the truth is, it will take more than a few years for us to solve challenges that have built up over decades.
"It will require common effort, shared responsibility, and the kind of bold, persistent experimentation that Franklin Roosevelt pursued during the only crisis worse than this one."
He laid out a set of goals in manufacturing, energy, education, national security and the deficit that he said would lead to jobs, opportunity and the rebuilding of the economy on a stronger foundation.
He said: "Our problems can be solved. Our challenges can be met. The path we offer may be harder, but it leads to a better place. And I'm asking you to choose that future. I'm asking you to rally around a set of goals for your country."
There was also a jibe at Mitt Romney's lack of foreign policy experience, highlighting the recent gaffe when he questioned London's preparedness for the Olympics.
Mr Obama said: "You might not be ready for diplomacy with Beijing if you can't visit the Olympics without insulting our closest ally."
The president trumpeted his own foreign policy and national security successes as he launched a blistering attack on his opponent, trying to persuade American voters he was the only candidate suitable of being commander-in-chief.
"In a world of new threats and new challenges, you can choose leadership that has been tested and proven," he said.
"I promised to refocus on the terrorists who actually attacked us on 9/11. We have. We've blunted the Taliban's momentum in Afghanistan, and in 2014, our longest war will be over.
"A new tower rises above the New York skyline, al Qaeda is on the path to defeat, and Osama bin Laden is dead."
Mr Obama warned Romney would fire teachers, impoverish students, all to give more tax breaks to millionaires.
"We've been there, we've tried that, and we're not going back. We're moving forward," he said, drawing raucous cheers from 15,000 people packed into a sports arena at the Democratic National Convention in Charlotte, North Carolina.
He referred to the promises of hope and change he made four years ago, which have been tested by the global financial crisis.
He said: "If you turn away now - if you buy into the cynicism that the change we fought for isn't possible - well, change will not happen."
He was joined on stage after the speech during a long ovation by his wife and daughters Sasha and Malia.