TAMPA, Fla. -- Republicans bestowed their presidential nomination on Mitt Romney on Tuesday, turning to the former Massachusetts governor and multi-millionaire businessman to drive Barack Obama from the White House and usher in a new era of small-government conservatism.

The overwhelming, enthusiastic vote of delegates at the Republican National Convention belied Romney's long, difficult road to the party's nomination: losing to Sen. John McCain four years ago and fending off a series of rivals in a brutal nomination fight this year. In the end, Republicans cast aside doubts about Romney's conservative credentials and bet that American voters would be persuaded that his business acumen was just what America needed in dreary economic times.

But Republican exuberance was tempered as Hurricane Isaac slammed into the southern Louisiana coast and headed toward New Orleans late Tuesday, striking the same region hit by Hurricane Katrina seven years ago. The storm prompted Republicans to cancel the first day of the convention. Though it no longer threatens Tampa, Republicans wanted to avoid holding a boisterous political celebration just as the storm was unleashing its fury.

With Romney's nomination now official, and Obama's assured at next week's Democratic convention in Charlotte, North Carolina, U.S. voters will face a clear-cut clash of ideologies: Romney, conservative on social issues such as gay marriage and abortion, favours cutting taxes, slashing the government and repealing Obama's signature health care overhaul -- even though it was modeled after one of his own programs as governor. Obama is liberal on social issues, wants to raise taxes on the wealthiest Americans and sees government as a potential force for good.

Polls show the race a dead heat, with the economy the top issue in the campaign. Voters say they trust Romney more on economic issues, but find Obama to be the more likable candidate.

Romney is scheduled to make his acceptance speech Thursday night, though those plans could be affected by the weather.

In the state-by-state roll call of convention delegates, Romney won 2,061 to 190 for Ron Paul, a libertarian-leaning Texas congressman. Paul's supporters chanted and booed after the convention adopted rules they opposed, but were powerless to block, to prevent those votes from being officially registered. "Shame on you," some of his supporters shouted from the floor.

The highlights of Tuesday's convention were the speech by Romney's wife, Ann, and the keynote address by New Jersey's outspoken governor Chris Christie, a star of the party. Both spoke during prime television time when all the major networks were airing the convention live.

Ann Romney's speech was meant to cast her husband, lampooned by comedians as robotic and denounced by Democrats as lacking compassion, in a soft and likable light. Romney was in the hall for her speech.

She lovingly talked of her 43-year marriage, noting her own experiences battling muscular sclerosis and breast cancer. She described her husband as a man who wakes up every day determined to solve the problems that others say can't be solved.

"This man will not fail," she said. "This man will not let us down."

Mitt Romney appeared on stage briefly at the end of the speech, kissing his wife, to wild cheers.

Christie's and Ann Romney's speeches followed a long series of addresses by other top party officials, praising Romney and blasting Obama. Reince Priebus, chairman of the Republican National Committee, said Obama has "never run a company. He hasn't even run a garage sale or seen the inside of a lemonade stand."

Rick Santorum, one of Romney's primary rivals, told the convention that under Obama, the American dream of freedom and opportunity has become a "nightmare of dependency" with almost half of the country receiving some form of government benefit.

Also, before nominating Romney, Republicans approved a party platform calling for cutting taxes as a way to stimulate the economy, ending abortion and repealing Obama's health care plan.

Congressman Paul Ryan, Romney's vice-presidential running mate, is scheduled to speak Wednesday. Republican delegates officially nominated him for the second-in-command spot on Tuesday night shortly after they named Romney.

While Republicans gathered in Florida, Obama campaigned in Iowa and Colorado as he set out on a tour of college campuses in hopes of boosting voter registration among college students, who tend to support him. Before departing the White House, he made a point of appearing before reporters to announce the government's latest steps to help those in the path of Isaac. He signed a declaration of emergency for Mississippi and ordered federal aid to supplement state and local storm response efforts in the state.