Republicans bestowed their presidential nomination on Mitt Romney, 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.

Polls show the race a dead heat, with the economy the top issue in the campaign

The overwhelming, enthusiastic vote of delegates at the Republican National Convention in Tampa, Florida, belied Mr Romney’s long, difficult road to the party’s nomination: losing to Senator 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 Mr Romney’s conservative credentials and bet that American voters would be persuaded that his business acumen was just what the country needed in dreary economic times.

But Republican exuberance was tempered as Hurricane Isaac slammed into the southern Louisiana coast early yesterday and headed towards New Orleans, striking the same region hit by Hurricane Katrina seven years ago.

The storm prompted Republicans to cancel the first day of the convention. Although it no longer threatens Tampa, Republicans wanted to avoid holding a boisterous political celebration just as the storm was unleashing its fury.

With Mr Romney’s nomination now official and Barack Obama’s assured at next week’s Democratic convention in Charlotte, North Carolina, US voters will face a clear-cut clash of ideologies.

Mr Romney, conservative on social issues such as gay marriage and abortion, favours cutting taxes, slashing the government and repealing Mr Obama’s signature healthcare overhaul – even though it was modelled after one of his own programmes as governor.

Mr 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 Mr Romney more on economic issues, but find Mr Obama to be the more likeable candidate.

In the state-by-state roll call of convention delegates, Mr Romney won 2,061 to 190 for Ron Paul, a libertarian-leaning Texas congressman. Mr Paul’s supporters chanted and booed after the convention adopted rules they opposed.

The highlights of the convention were the speech by Mr 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 US television time when all the major networks were airing the convention live.