Starting today, Thompson will spend the next week in the key early primary states of Iowa, New Hampshire, South Carolina and Florida.

He's betting he can make up for lost time and convince skeptics in his party that he's neither lazy nor underprepared, but instead methodical and getting in just as voters are ready to pay attention. All of his major competitors have spent months courting voters, raising money and refining their stances.

"He could catch fire and take off," said Cary Covington, an associate professor of political science at the University of Iowa. "But, historically, candidates who rely in Iowa on television ads and commercials don't do well. It takes organizing at the grassroots level and that takes time, and Thompson just doesn't have much of that time left now. He can't afford any mistakes. He has to hit hard and charge hard and really be running full blast."

Thompson has strengths going in. He's got celebrity and a homespun appeal as well as experience in national politics. He's also got a socially conservative message and reputation that could appeal to his party's base.

So far, Republicans have yet to solidify around any single competitor, be it former New York Mayor Rudy Giuliani, former Massachusetts Gov. Mitt Romney or any of the others.

Recent polls in early primary states show Thompson in second or third place among GOP candidates, in some combination with Giuliani and Romney.

Yet with his announcement, Thompson is off to mixed reviews.

Thompson's timing allowed him to avoid participating, literally by a few hours, in a televised Wednesday night candidate debate in New Hampshire. But his campaign bought time on Fox to air a 30-second Thompson spot during the debate.

That prompted New Hampshire's Republican Party chairman to accuse Thompson of wanting it both ways.

"I think New Hampshire voters and voters elsewhere would be forgiven for thinking he's skipping the debate because he isn't ready to have a substantive debate on the issues," chairman Fergus Cullen said. "And voters also could be forgiven for thinking, 'Well, what the heck was he doing all summer if he wasn't preparing?' There's a genuine interest here in Sen. Thompson and curiosity. But he seems to be getting off on the wrong foot."

Thompson's communications director Todd Harris defended the strategy. "We're not skipping debates," Harris said. "We're going to be present at a number of debates" in New Hampshire and other states in the weeks and months ahead.

"It's a question of how we've decided to roll out our campaign. And this is how we've decided to do it.

"Jay Leno is one of the highest-rated shows on television, and Sen. Thompson's message is going to be about bringing the country together under a banner of mainstream conservative change," Harris said. "You can't talk about unifying the country without talking to the entire country."

Harris describes Thompson as "the best communicator of the mainstream conservative message" in the GOP. "And our party needs a good communicator at a time when many in the public are not as high on the Republican Party as they used to be," he said.