TAMPA, Florida (AP) - Republican Mitt Romney, in the most important speech of his presidential campaign, told a television audience of millions that Barack Obama had failed to deliver on his soaring promises of hope and change and that it is time for new leadership during tough times in America.
Mr Romney accepted the Republican presidential nomination late on Thursday, casting himself as the best hope to lift the struggling US economy and "restore the promise of America". He outlined lofty goals - making the US energy independent, slashing the deficit, and creating 12 million jobs - though said little about how he would achieve them.
"President Obama promised to begin to slow the rise of the oceans. And to heal the planet. My promise is to help you and your family," he said.
His speech marked the climax of the three-day Republican National Convention and a milestone in his long, often-rocky quest for the presidency. Four years ago, he was defeated by John McCain in his bid for the nomination. This year, 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 per cent 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.
Those words were clearly not directed at the Republican audience before him, but to television viewers who had backed Mr Obama in 2008. Mr Romney will need to win many of them over if he is to have a chance at winning the White House.
The speech was seen as a national introduction of sorts for the 65-year-old - an oddity considering his years in the public eye. 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 - unfairly, friends say - 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 likable.
The campaign hoped the convention would change perceptions. For three days, speakers have portrayed the candidate as a man of family and faith, savvy and successful in business, savior 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 offered details of his family life, recounting his youth as a Mormon, the son of parents devoted to one another, then a married man with five rambunctious sons.
He choked up at least twice, including when he recalled how he and wife Ann would awake to find "a pile of kids asleep in our room."
Before Mr Romney's speech, church members warmly presented him as a compassionate man who lives his Mormon faith of service. Grant Bennett described Mr Romney's volunteer work shovelling snow and raking leaves for the elderly. A couple, Ted and Pat Oparowski, recalled how Mr Romney befriended their 14-year-old son David as he was dying of cancer. "We will be ever grateful to Mitt for his love and concern," she said.
Mr Romney is the first Mormon nominee of a major US political party.
Republicans also turned to some Hollywood firepower, with Clint Eastwood, the legendary tough guy, taking a turn at the podium. "When somebody does not do the job you've got to let `em go," he said to a roaring audience.
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.
Veering from the speech's focus on domestic affairs, Mr Romney said Mr Obama failed to slow Iran's nuclear threat, abandoned Poland by changing missile defence plans and has "thrown allies like Israel under the bus." He said Mr Obama is "eager to give Russia's president (Vladimir) Putin the flexibility he desires after the election."
"Under my administration, our friends will see more loyalty and Mr Putin will see a little less flexibility and more backbone," he said.
When his speech ended, Mr Romney was joined by running mate Paul Ryan, then their wives, and finally a stage full of their children and grandchildren. Confetti and thousands of red, white and blue balloons floated down from the rafters.
Cheering him on were the thousands of Republican delegates who overwhelmingly approved his nomination in a roll-call vote Tuesday. The party has rallied behind Mr Romney despite longstanding concerns about his shifting political positions and doubts about whether he was a true conservative. Mr Romney's religion also unsettled some evangelicals who do not see Mormonism as a true Christian faith.
But the Republican desire to evict Mr Obama from the White House overwhelms any trepidation about Mr Romney. Moreover, the party was thrilled when he picked congressman Paul Ryan, the architect of a plan to slash government spending, as his vice presidential running mate. Mr Ryan delivered a rousing acceptance speech on Wednesday.
The two-month campaign to come includes other big moments - principally a series of one-on-one debates with Mr Obama. More than $500 million has been spent on campaign television commercials so far. Mr Romney has raised more than Mr Obama.
Democrats looked to use Ryan's speech to fundraising advantage, highlighting factual errors. In a letter sent to potential donors, Obama campaign manager Jim Messina said the Ryan speech "represents a huge bet by the Romney campaign - they've decided that facts, truth and reality will not be a brake on their campaign message."
The president himself was staying out of the spotlight on Thursday. But in an interview with Time magazine released on Thursday, Mr Obama 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."