US Republicans have formally nominated Mitt Romney to challenge President Barack Obama for the White House.
The nomination kicked off their storm-delayed convention with a barrage of sharp attacks on Mr Obama's economic leadership and set up a two-month dash to the 6 November election.
Polls show Mr Romney running even or slightly behind the Democratic president.
Republicans repeatedly accused Mr Obama of being hostile to small business owners, burying them under high taxes and excessive regulations that stunted job growth.
His signature healthcare overhaul, they said, was big government run amok.
"It's time to end this era of absentee leadership in the Oval Office and send real leaders to the White House. America needs Mitt Romney and Paul Ryan and we need them right now," said New Jersey Governor Chris Christie, who delivered the convention's keynote address.
"Mitt Romney will tell us the hard truths we need to hear to put us back on the path to growth and create good-paying private sector jobs again in America," he said.
Republicans are using the convention to make the case for booting Mr Obama from office while presenting a softer side of Mr Romney.
Mr Romney has struggled to overcome a "likability gap" with the president and refute critics who paint him as a job-killing, out-of-touch former private equity executive.
Mr Obama, campaigning in Iowa and Colorado, dismissed the Republican attacks and told a rally in Ames, Iowa, that the agenda his political foes were rolling out in Tampa made for a "pretty entertaining show".
He also accused Republicans of stretching the truth in a multi-million-dollar ad effort to get him out of the White House.
"They'll just make stuff up if they have to. They're doing it already," he said at an event in Fort Collins, Colorado.
"Sometimes - how do I put this nicely? - they will just fib."
Polls show Mr Romney trails Mr Obama badly with women voters, and the convention featured a series of women speakers capped by Mr Romney's wife, Ann.
She said her husband had attacked every challenge - from reviving the struggling Salt Lake City Olympics to helping her battle multiple sclerosis and breast cancer.
"A storybook marriage? Nope, not at all. What Mitt Romney and I have is a real marriage," she said in a speech timed to air during the one hour of prime-time coverage by US broadcast television networks. "You can trust Mitt."
The former Massachusetts governor, who flew to Tampa earlier in the day, came onstage and gave his wife a kiss after her speech, getting a rousing reception from delegates.
