Mitt v Isaac in Tampa

The convention's start has been delayed because of the approaching storm

At St Pete's beach, a woman - a towel wrapped around her bikini - lounges in a deck chair staring out to sea at the ominous black clouds.

At a North Tampa Walmart, shoppers - more provident than fearful - push baskets laden with gallons of water recommended by the Federal Emergency Management Association.

On TV, presenters joke that perhaps Mother Nature is a Democrat.

The threat of Tropical Storm Isaac has delayed the start of the Republican convention, but you wouldn't know it inside the hall where it will all happen.

The house band blast out a sound check, CNN's Wolf Blitzer rehearses a walk and talk for his show. Everything in the vast auditorium is bathed in blue and red lights, atmospheric, but curiously reminiscent of emergency vehicles at a crash scene.

Still, Republicans are crossing their fingers that there'll be no accidents this week. They hope that Isaac will miss and Mitt will be a hit.

Mitt Romney has a tricky path to walk in Tampa

He's tweeted his approval of the delay to the meeting, which means he won't be officially nominated on Monday: "The safety of those in Isaac's path is of the utmost importance. I applaud those in Tampa making appropriate schedule changes."

He may not applaud all the statements coming from the floor when the convention does kick off. He has a tricky path to walk.

He might want to convince the conservative base that he really is one of them. But he doesn't want to play into the hands of the Democrats who are determined to depict him as a scary reactionary in thrall to nutters and cranks.

That campaign is getting more intense.

President Obama, apparently determined to distract attention from the economy, said in an interview this weekend that Romney had "signed up for extreme positions".

The Obama campaign team pulled out all the stops to link Romney's name to that of the once obscure congressman Todd Akin, who coined the ugly phrase "legitimate rape".

By the time they were through, the uninformed might think Todd Akin was the third name on the ticket.

The president's campaign went into overdrive to highlight an awkward joke Mr Romney made about his birth certificate, suggesting he had strayed into "birther" territory.

The president once found the accusation that he wasn't born in the USA an irritating distraction.

Now he wants to highlight it, even producing a new badge to go with the existing mug for his followers, featuring the slogan "Made in the USA" and a picture of his birth certificate.

The Republicans must hope Isaac doesn't blow them off course - there's even talk of further delays if the storm heads to New Orleans.

But they've already been buffeted off message in the last week by Mr Obama's accusations.

They need to find a way to counter the charge of extremism, so the tone coming out of Tampa this week is all important.