Rudy Giuliani had a big decision last week: How to thank Ron Paul for helping him win the Republican debate Tuesday night.

Paul did it by feeding New York’s former mayor a big fat slow pitch right down the middle of the plate, and Giuliani promptly smashed it out of the park.

Home run, debate over.

Paul, the old-timey Texas crank in the 10-man field, certainly didn’t mean to help anyone. Pushing his line that true conservatives should oppose an expansive foreign policy, Paul suggested that 9/11 was a direct result of our policies in the Mideast.

Bingo. Giuliani, who had mostly been on the defensive over his support for abortion rights, gun control and gay rights, quickly jumped to respond. His face taut and fairly bristling with anger, said, “As someone who lived through the attack of Sept. 11,” he had heard many absurd things about 9/11, but nothing like Paul’s idea “that we invited the attack because we were attacking Iraq.”

The crowd at the University of South Carolina loved both the answer and the genuine outrage. As soon as the applause stopped, Giuliani wisely turned the heat back on Paul by asking the “congressman to withdraw that statement.”

Paul didn’t, of course, but that’s his problem. Giuliani got exactly what he needed – a chance to change the subject and get back on the terror turf.

He’s been trying to do that ever since he muffed his answers on abortion in the first debate. Since then, he went a long way in clarifying his position in a well-received speech in Houston and has clearly decided he’s not going to waffle.

But being pro-choice won’t win him the nomination. The best he can do is hope that it doesn’t lose it for him. Tuesday night he put on a clinic about how to maximize your strengths so that your negatives are diminished.

He’s still pro-choice, but he’s tough and certain on terror, and that’s his ticket.

The other top contenders were not as successful in the lively exchange, which was well-staged to let the candidates do most of the talking. John McCain struggled to maintain his upbeat, can-do demeanor and looked momentarily rattled when Mitt Romney criticized McCain’s position on immigration and campaign financing. McCain seemed to be biting his tongue at the audience applause and answered with a broadside against money that included the phrase the “corruption of our own party.” That could be a loser in South Carolina, where McCain is not beloved to begin with.

Romney had another solid performance, and it’s easy to see him gaining modest traction with each appearance. He’s quick and smart and has made a good impression in both debates. Still, some GOP regulars demand fresh faces. Former Sen. Fred Thompson, who’s best known as a TV actor in “Law & Order,” has been flirting around the edges for months, but still hasn’t gotten in. And Newt Gingrich is making noises again about running, saying there is a “great possibility” he, too, would join the fray.

Hey, come one, come all. Just don’t try to exclude Ron Paul, Rudy Giuliani’s new best friend.