John McCain emerged in a naval yard here on the eve of today's critical Republican primary to rousing military band music. Surrounded by national security experts, the former Vietnam prisoner of war called Islamic extremism “the great challenge of our time”, talked up his recent endorsement by General “Stormin' Norman” Schwarzkopf, of first Gulf War fame, and with a menacing laugh accused Mitt Romney of having “flip-flopped on every issue”.

Nearly 300 miles away Mr Romney, locked in a dead heat with his rival, gathered a crowd at a West Palm Beach petrol station to call Mr McCain a “liberal Democrat” when it came to the economy, a subject, he has said repeatedly in recent days, that Mr McCain “does not understand”. On Sunday he called Mr McCain a liar for accusing him of having advocated a timetabled troop withdrawal from Iraq last year — something that the former Governor of Massachusetts denies.

Should the people of Florida be in any doubt that the Republican presidential race appears to have come down to two candidates who dislike each other intensely, and their competing messages of terrorism versus the economy, the performances of Mr McCain and Mr Romney in the past 24 hours could not have been clearer.

If recent polls are borne out tonight, Rudy Giuliani, the former New York Mayor, and Mike Huckabee, the winner of Iowa, will trail badly behind the two front-runners, defeats that might end both campaigns. Unlike other early and inconclusive contests, however, Florida's primary could all but decide the nomination.

Victory for Mr Romney would propel him on to “Super Tuesday” a week later, when 22 states vote, with huge momentum. Unlike Mr McCain, he has a huge war chest - backed by his own fortune of $250 million (£126million) — to swamp the airwaves across the country on February 5. A McCain victory will probably send the Republican Establishment rallying behind the Arizona senator, leaving any chance of stopping him from winning the nomination extremely difficult.

In this increasingly intense and personal battle — Mr McCain does little to hide how much he despises his Brylcreemed rival — the men have boiled their messages down to two competing themes. Mr McCain is trying to attract voters by sounding almost apocalyptic about Islamic terrorists, arguing that he is the only candidate with the experience and judgment to defeat them.

He cites his early and persistent calls for an Iraq “surge”, when his rivals equivocated on the subject, as proof of his courage and prescience. His advantage in Florida, heavy with air strips, naval stations and barracks, is that 40 per cent of the state's voters have ties to the military. He also received the weekend endorsement of Charlie Crist, Florida's hugely popular Republican Governor.

Mr Romney, by contrast, a Harvard Business School graduate who has approached his candidacy like a product launch — find what message sells and mass-market it — has finally stumbled upon a winning sales pitch, courtesy of a serendipitous piece of timing: the sudden fears of a recession. Mr McCain is desperately trying to steer the subject back to Iraq at a time when it is fading from voters' minds.

Having torn up his campaign billboards that proclaimed “strength” and “optimism”, Mr Romney has appeared in Florida in recent days before banners declaring “economic turnaround”. He emphasises his business experience, telling voters: “I spent my life doing what you are doing, working in the real economy.”

He says that he knows how to bring back the economic good times — he won his native state of Michigan with such a message.

Asked about Mr McCain's accusations that he advocated a troop withdrawal date from Iraq — a claim that is misleading at best — Mr Romney called it dishonest, adding: “He's doing everything he can to try to divert attention away from his lack of understanding of the economy. There is no way someone can lead this country without understanding the economy.”

Mr McCain has fought his way back into contention after his campaign fell apart in the summer, with victories in New Hampshire and South Carolina. He bristles at Mr Romney's reversals on issues such as abortion, gay marriage and gun control, and the chameleon-like way in which he campaigns before different audiences.

“One thing I think we should give Governor Romney credit for,” Mr McCain said with a sneer. “He's consistent. He has consistently taken both sides on every issue. And that's why we're going to win Florida and Super Tuesday.”

For the anoraks

Barack Obama's speech in Washington yesterday was not merely a convenient place to pick up the endorsement of Edward Kennedy. Although DC voters are denied a voice in congressional elections, they do get to participate in presidential contests - including the nomination process. Washington, along with its neighbours Maryland and Virginia, vote on February 12 in what has been billed the "Potomac primary". A total of 239 Democrats and 119 Republican delegates are at stake.

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