THE Republican frontrunner, Rudolph Giuliani, is to highlight Fred Thompson’s lack of experience after the former Tennessee senator and actor officially entered the race for the presidential nomination last week.

Giuliani, the former mayor of New York, gave a preview of his tactics during a Republican candidates’ debate in New Hampshire when he said Thompson had “done a pretty good job playing my part on Law & Order”.

Thompson is best known in America as Arthur Branch, a gruff, conservative New York attorney in the television crime series Law & Order. The screen-writers are working out how to write him out of the plot, as campaign rules forbid him from appearing on screen. Giuliani is doing the same.

A source close to the Giuliani campaign said he would contrast his experience as a welfare reformer, tax-cutter and crime-beater in America’s toughest city with Thompson’s record of having named a few post offices while he was a senator.

Thompson, 65, performed well on The Tonight Show with Jay Leno last week, where he declared to laughter that his “wrinkles” did not come from testing the water for a presidential run for too long. Some of his supporters were delighted that he was reaching an audience of ordinary voters while his rivals were slugging it out in a debate watched by political junkies.

But to others it suggested his campaign was not serious. “I’m willing to be enthusiastic about a Thompson presidency, but only if he is,” said one former supporter.

Adding to doubts about his managerial experience, Thompson has seen his campaign team rocked by half a dozen high-profile departures in the past month. Mark Corallo, who launched Thompson’s informal presidential bid last spring, resigned in frustration last week after another well-regarded colleague, Jim Mills, a former Fox News producer, was sidelined and quit.

Several appointees gave up good jobs to commit to Thompson and have been left high and dry, creating much ill-feeling. In contrast, Giuliani’s tightly knit team includes long-term aides who have worked with him since the 1990s. He is also bringing in advisers with strong links to Christian conservatives and the gun lobby, two powerful groups in the Republican party that are sceptical of Giuliani’s pro-choice record on abortion and his antigun policies in New York.

Thompson has already taken a shot at Giuliani’s gun control measures as mayor. “When I was working in television, I spent quite a bit of time in New York City,” he said. “There are lots of things about the place I like, but New York gun laws don’t fall in that category.”

Giuliani and Thompson both claim to be the only Republican candidate who can beat Hillary Clinton, the favourite for the Democratic nomination. Thompson intends to contrast his affable, Southern gentleman style with her alleged divisiveness.

“You don’t want to have to come back from another Clinton victory,” he told supporters in Iowa last week. “Our country needs us to win next year, and I’m ready to lead that effort.”

Terry McAuliffe, Clinton’s campaign chairman, said that after working for Jimmy Carter’s failed bid for re-election against Ronald Reagan, “I’m never underestimating another B-movie actor.”

Larry Sabato, professor of politics at Virginia University, said Thompson had had “a better launch than expected” but that had been the easy part. “He had months to prepare for it and go on the Leno show and get [thrown] softballs.”

Sabato predicted Thompson would suck the oxygen from his fellow conservative Mitt Romney, the Mormon former governor of Massachusetts, without hurting Giuliani’s support all that much. “Giuliani has surprised me,” he said. “I never thought he would prove that durable.”

Clinton appears to be cruising to the Democratic nomination, having opened up a lead of 18 points over Barack Obama, her closest rival. But the power of the broadcaster Oprah Winfrey to shift voters to Obama will be tested this weekend after she hosts a star-studded fundraiser for the Illinois senator at her $50m mansion in California. The latest Rasmussen tracking poll shows Giuliani leading Thompson by 24 points to 23. Romney is on 14 and Senator John McCain on 11.

The race is on between the top two to pick up the votes of the other candidates. Giuliani said he would vote for McCain if he were not standing himself, in a clear pitch to win his rival’s supporters. Thompson supporters hope to pick up votes from Romney, on the grounds that their candidate is a stauncher conservative, with no Mormon baggage.

Thompson announces his decision to stand: click here

Giuliani fires television debate: click here

For latest polls in key states: click here

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