Barack Obama has failed to deliver on his promise of hope and change and it is time for new leadership in the White House, Mitt Romney told America, in the most critical speech in his presidential campaign.
Mr Romney accepted the Republican presidential nomination, casting himself as the best hope to lift the struggling US economy and "restore the promise of America".
His speech marked the climax of the three-day Republican National Convention and a milestone in his long, often-rocky quest for the presidency. He had to fend off a series of Republican challengers, questions about his shifting positions and mutterings about his Mormon religion.
The ultimate prize, the White House, will be determined in a November vote. Polls show Mr Romney and Mr Obama in a dead heat with the economy the biggest issue in the campaign. The United States is struggling with 8.3% unemployment and the slowest economic recovery in decades.
Mr Romney noted excitement over Mr Obama's promises from his campaign four years ago "gave way to disappointment and division". "You know there's something wrong with the kind of job he's done as president when the best feeling you had was the day you voted for him," he said.
The speech was seen as a national introduction of sorts for Mr Romney, 65. Yet for all his time as candidate, Massachusetts governor and head of the 2002 Winter Olympics in Salt Lake City, he remains something of an enigma. He is often seen as stiff and distant.
While polls show voters view Mr Romney, a multimillionaire former businessman, as more capable of fixing the economy, they find Mr Obama to be more honest and likeable.
The campaign hopes the speech and the convention in general will change perceptions of Mr Romney. Speakers have portrayed the candidate as a man of family and faith, savvy and successful in business, saviour of the 2002 Winter Olympics, yet careful with spending. A portion of the convention stage was rebuilt overnight so he would appear surrounded by delegates rather than speaking from a distance, an attempt to soften his image.
Mr Romney made a press-the-flesh entrance into the hall, walking slowly down one of the convention hall aisles and shaking hands with dozens of delegates. The hall erupted in cheers when he reached the stage and waved to his cheering, chanting supporters before beginning to speak. "I accept your nomination for president," he said, to more cheers.
Mr Obama himself was staying out of the spotlight. But in an interview with Time magazine released on Thursday, the President said he was hopeful for a more productive second term if re-elected, because "the American people will have made a decision. And, hopefully, that will impact how Republicans think about these problems."