Many doubt he can catch the front-runners with such a late start in raising money, organization and endorsements. He responds that "it's too late to follow those rules even if I wanted to, and I don't want to." Instead he plans to use new technology in innovative ways that include everything from the Internet to distributing videos to cell phones. Less tech-savvy primary voters can expect to see Mr. Thompson as a constant presence on talk radio and cable TV news. Will that be enough? Much of it may depend on just how much Mr. Thompson can build on the success of Howard Dean in 2004 in harnessing the power of the Internet as a fund-raising tool.

One obvious shortcoming is that Mr. Thompson hasn't run for office since 1996. After he announces and enters the maelstrom of a national campaign, he will inevitably make mistakes, misspeak and demonstrate a lack of knowledge on issues the other candidates have had months to bone up on. How he handles adversity and crises on the campaign trail will be the true test of his mettle and adaptability.

His competitors will no doubt belittle Mr. Thompson's eight years in the Senate as lackluster. Few bills passed bearing his name as a chief sponsor. Mr. Thompson told the Associated Press that he plans to correct the record by pointing out that a senator's accomplishments don't "always have to do with putting your name on a piece of legislation. There was an awful lot of bad legislation that I helped to stop for one thing."

A related charge is that he was something of a slacker, both in his Senate duties and in campaign fund-raising. But the evidence for this claim is thin. Norman Ornstein, a congressional scholar at the American Enterprise Institute, told Reuters that he saw Mr. Thompson as a thoughtful lawmaker who reached across party lines: "He worked plenty and he absorbed plenty." For his part, Mr. Thompson says "that's one rap you can cure," by showing his energy level as he courts voters and as contributors respond to his appeals.

As for his ambivalence about running for president until age 64, he jokes that voters may like someone "who hasn't lusted for the job since they were student body president." He maintains that "if a person craves power for the sake of power, if he craves the office for the sake of holding the office, he's got his priorities mixed up. It [should be] a desire to do something not be something."

Mr. Thompson will run an unorthodox campaign, one that will challenge the conventional wisdom about how to run for president. Even if it proves unsuccessful, it's useful for a candidate to occasionally come along and ask if the rules everybody is following were made for a different time and new approaches are appropriate.

That attitude is part and parcel of the innovation and injection of new blood that animates so much of American life, and from Barack Obama on the left to Fred Thompson on the right, it's a healthy development that this year's presidential election is seeing different kinds of candidates.