Kiichiro Sato, Associated Press
John McCain, left, Mitt Romney, Fred Thompson and Rudy Giuliani speak to each other before the debate in Dearborn, Mich.

DEARBORN, Mich. (MCT) — Rudy Giuliani and Mitt Romney traded the sharpest shots of the campaign Tuesday night over who's the bigger tax-cutter, with Romney dismissing one Giuliani claim as "baloney" and the ex-mayor saying flatly, "I led, he lagged."

Their testy and at times even personal tone threatened to overshadow the debate debut of Fred Thompson, who likely quieted critics of his early campaign stumbles with a sure-footed if hardly flashy performance.

"I've got to admit, it was getting a little boring without me," the "Law and Order" actor joked of his late entry into the race.

But it was the former mayor and the former governor — not the former Tennessee senator — who provided the debate's sparks, as Giuliani and Romney notched up the intensity of their attacks compared to earlier debates, a sign that the race is moving ever closer toward its critical phase.

Romney attacked Giuliani for launching a lawsuit as mayor to block the presidential line-item veto — a seemingly obscure topic dear to anti-tax conservatives, who believe the ability to kill individual budget items would chop federal spending.

Giuliani tried to turn the attack on its head, noting that he sued President Bill Clinton to preserve $250 million in city funding and won in the Supreme Court. "I don't think it's a bad idea to have a Republican presidential candidate who actually has beat President Clinton at something," he said.

Giuliani in turn charged that state spending and taxes went up while Romney was Massachusetts governor, and city spending and taxes went down while he was mayor.

"The point is that you've got to control taxes, but I did it, he didn't," Giuliani said.

Romney shot back: "It's a nice line, but it's baloney. Mayor, you've got to check your facts."

Both camps last night proclaimed themselves pleased with the tough exchanges. Romney's campaign believes Giuliani's lawsuit shows he is out of step with Republican orthodoxy. Giuliani's team likes talking about his fiscal record, hoping it can win over conservatives turned off by his stances on abortion and gun control.

For Thompson, the debate was a chance to give his presidential campaign a bit of a jolt, to use a national stage to put to rest the story line — which even broke into a "Saturday Night Live" sketch this week — that he's an indifferent campaigner, not committed to working hard enough to get the nomination and perhaps undeserving of a spot in the top tier.

He offered a solid performance free of gaffes or major gaps and displayed some of the down-home charm that attracted Republicans longing for the southern conservatives the race has lacked until now. By debate's end, Thompson seemed to warm to his role a bit, jabbing Romney after Romney trotted out a joke on Thompson's "Law and Order" role.

"Not bad, not bad. And to think I thought I was going be the best actor on the stage," Thompson said.