| TAMPA, Florida
TAMPA, Florida Republicans nominated Mitt Romney on Tuesday to challenge President Barack Obama for the White House, kicking off their storm-delayed convention with a barrage of sharp attacks on Obama's economic leadership.
The formal nomination of Romney and his running mate, Paul Ryan, sets up a two-month final dash to the November 6 election. Opinion polls show Romney running even with or slightly behind the Democratic president.
The convention's opening was pushed back a day by a storm threat, but Republicans wasted no time in condemning Obama's economic record and reminding voters of the stubbornly high national unemployment rate and growing budget deficit.
Reince Priebus, chairman of the Republican National Committee, warned that re-electing Obama would mean "four more years of failure."
"We have a message for America: Elect Mitt Romney and Paul Ryan and they'll get America working again," he said to loud cheers. "We must send America's comeback team to Washington."
But as Republicans tried to show a united front against Obama, it was clear on Tuesday that bitter divisions within their party have not been resolved.
Supporters of libertarian congressman Ron Paul of Texas and other conservative activists briefly disrupted the opening session, booing a decision to unseat Paul delegates from Maine and institute rules changes they believe will weaken their power in the next election cycle.
The rules changes, approved by the convention on a voice vote, will bind delegates to the results of a statewide vote and reduce the role of smaller state-level conventions where Paul had success.
Opponents of the move said that Romney's operatives and the party's establishment were trying to freeze them out. Some noted that in the state-by-state roll call of delegates to count votes for the presidential nomination, only Romney's vote totals were announced from the podium.
"We were disenfranchised by our party. We won't participate with this chaos," said Russell Montgomery, 52, of St. George, Maine. "We won't legitimize this fiasco. This is as bad as the other party - the corruption."
The opening night will be capped by prime-time speeches by Romney's wife, Ann, and New Jersey Governor Chris Christie.
Romney, who had originally planned to stay out of the spotlight until Thursday night when he accepts his party's nomination, made an early appearance in the Florida host city to be on hand for his wife's turn at the podium.
Republicans hope to use the convention to make an aggressive argument for booting Obama from office while presenting a softer side of Romney, who is struggling 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.
In excerpts of her speech, Ann Romney said her husband has attacked every challenge he has faced - from reviving the struggling Salt Lake City Olympics to helping her battle multiple sclerosis and breast cancer.
"At every turn in his life, this man I met at a high school dance has helped lift up others," Romney, 63, will tell the convention.
"This is the man who will wake up every day with the determination to solve the problems that others say can't be solved, to fix what others say is beyond repair," she said. "This is the man who will work harder than anyone so that we can work a little less hard."
Republicans have hoped their convention will not be overshadowed by Hurricane Isaac, forecast to hit in the New Orleans area seven years after it was devastated by Hurricane Katrina. They also have worried about being seen celebrating Romney's nomination while swathes of the Gulf Coast were under storm threat.
While Tampa was spared the brunt of Isaac, a destructive landfall in Louisiana in the next day or so could create uncomfortable split-screen television images of the convention juxtaposed with the hurricane.
The Republican gathering will culminate with Romney's nationally televised acceptance speech on Thursday, the biggest speaking engagement of his political life.
Obama, campaigning in Iowa and Colorado, dismissed the Republican attacks and said the agenda his political foes were rolling out in Tampa made for a "pretty entertaining show."
He said Romney's economic plan would benefit the rich at the expense of the middle class.
"In just over two months, you will make a choice about which path we take, and it's going to be a stark choice," he told a campaign rally at Iowa State University in Ames, Iowa.
The Republicans' headline speakers later on Tuesday night are expected to keep making their party's case against Obama while arguing that Romney could do a better job.
Expectations are high for the keynote speech by Christie, New Jersey's confrontational governor, which is likely to be heavy on red-meat rhetoric for conservatives.
Many Republicans like Christie's in-your-face style, which contrasts with Romney's stiff demeanor and has made him a rising political star.
"You start turning it around tonight," Christie told ABC's "Good Morning America" program when asked how to overcome some voters' lack of enthusiasm for Romney.
Vice presidential contender Ryan, a Wisconsin congressman, tops the bill of speakers on Wednesday.
(Additional reporting by Steve Holland, Andy Sullivan, Sam Youngman and Sam Jacobs; Editing by Alistair Bell and Leslie Adler)