Republican Fred Thompson on Tuesday mocked rival Mitt Romney for spending millions of his own money on the presidential race.

"Governor, you can't buy South Carolina," Thompson told about 200 people at a restaurant. "You can't even rent South Carolina."

Romney, a former venture capitalist and one-time Massachusetts governor, has dipped into his personal wealth for nearly $17.5 million and has spent about $2 million on advertising in South Carolina. He has reported a personal wealth of between $190 million and $250 million.

Romney said he was putting in the hard work that is necessary to win a state like South Carolina. That was his way of suggesting that Thompson, regarded by some as a lazy candidate, was living up to his reputation.

"What you have to do to get South Carolina is you have to work it. That's why I have made so many trips here, over 50 events in South Carolina," Romney said. "When he catches up to me in events, then he'll know he's got South Carolina, too, but you have to work South Carolina. That's what I have been doing over the past year.

Overall, Romney has raised about $45 million for his White House bid since the start of the year. Thompson, who didn't enter the race until this summer, has raised about $13 million.

Thompson focused on Romney's spending on the same day he launched television ads in Iowa and on Fox News Channel that will cost several hundred thousand dollars.

In South Carolina, Thompson said he hadn't bought a single ad and yet led Romney in a recent state poll. "So, you know, from a management standpoint, I think I'm getting a little bit more for my money right now," Thompson said.

Thompson also criticized his rivals, in particular Arizona Sen. John McCain, for support of a failed immigration bill that was backed by President Bush.

"And of the so-called top-tier candidates, every one of my opponents in this race supported that bill, except me," Thompson said.

The former Tennessee senator misspoke. In fact, none of the other Republican candidates supported McCain's immigration bill this year, with top candidates Rudy Giuliani and Romney criticizing the measure at various debates and campaign stops.

Thompson is the first Republican candidate to directly criticize Romney's wealth. Former Arkansas Gov. Mike Huckabee has alluded to the spending by other campaigns, rejecting the notion that big money is essential.

"People have said you have to have this much money to be competitive and they've been wrong," he said. "A lot of these campaigns have spent an enormous amount of money. We have been frugal and make no apologies for that."

Thompson also responded to questions about whether he has enough "fire in the belly," saying he thinks it's more important for a president to have sound judgment and credibility.

"Ultimately the American people have to ask themselves do they want someone with their finger on the nuclear button who has fire in his belly — or her belly," Thompson said.

Thompson's last stop Tuesday was at The Beacon, a Spartanburg burger joint that is a rite of passage for political candidates in South Carolina.

"I understand that in order to be president of the United States, you've got to come to the Beacon, so I'm here," Thompson said.

He later stood in line with others waiting to order chili cheeseburgers and onion rings.