It’s been four years since Rudy Giuliani joined Sen. John McCain to launch the GOP convention in the strategically chosen city of New York.

There, the former mayor somberly recalled his memories of Sept. 11, 2001, and both men talked glowingly about President Bush’s leadership during and after the terrorist attack.

McCain’s national security credentials are one of the Republican presidential candidate’s strongest assets. Throughout the campaign, McCain has been unwavering in his belief that Bush’s overall foreign policy approach is the right one for the country, and has warned that Sen. Barack Obama (Ill.), the Democratic nominee, would undo much of the success the U.S. military has achieved in Iraq and would lead the nation backward in the fight against global terrorism. McCain is almost certain to convey that same message when he formally accepts the party’s nomination.

Until his descent from atop the national polls in 2007 forced him out of the running for president, Giuliani hoped to be delivering that very speech in St. Paul Thursday night.

But his role as keynote speaker gives him a chance to redeem himself to the party faithful after a disappointing campaign. It also gives him a chance to remind Republicans that, while he may not be the darling of the conservatives, his stature as someone with direct knowledge of the dangers of terrorism is invaluable to a party intent on again making national security a central tenet of its 2008 platform.

In that role, there may be no one better.

“On Sept. 11, this city and our nation faced the worst attack in our history,” the former New York mayor said in his speech at the 2004 GOP convention. “On that day, we had to confront reality. For me, standing below the North Tower and looking up and seeing the flames of hell and then realizing that I was actually seeing a man — a human being — jumping from the 101st or 102nd floor drove home to me that we were facing something beyond anything we had ever faced before.

“At the time, we believed we would be attacked many more times that day and in the days that followed,” Giuliani continued in a speech that brought deafening silence to a normally boisterous crowd. “Without really thinking, based on just emotion, spontaneously, I grabbed the arm of then-Police Commissioner Bernard Kerik and I said to him, ‘Bernie, thank God George Bush is our president.’ ”

After dropping out of the 2008 race without a single delegate won, Giuliani immediately embraced McCain as the man best suited to build on the Bush legacy. That won the former prosecutor praise from the party and cemented his standing with the senior senator from Arizona.

Giuliani has since campaigned tirelessly for McCain, and even volunteered to plunge into enemy territory last week and provide rapid response to those Democrats taking prominent speaking roles at the convention in Denver.

Yet some of Giuliani’s ardent support has not been exactly what the McCain campaign has needed.

It was, in fact, Giuliani who suggested to reporters on a conference call that McCain would not necessarily disqualify someone for vice presidential consideration because of an abortion-rights stance. And he even went so far as to say that the Republican Party would be able to support such a choice — a line that many conservatives were not comfortable with either McCain or Giuliani crossing for them.

McCain has had his own troubles winning the hearts, if not still being able to win the minds, of conservatives. But it was Giuliani, who is thrice divorced and has a mixed policy record on abortion and gay marriage, who was viewed as the blackest of the sheep among evangelicals and conservatives watching the Republican primary.

Although Giuliani failed to convince them that he would be the GOP’s best chance at retaining the White House in 2008, he has never once failed to carry out a mission that is just as important as carrying the party’s flag: Tearing the other party to pieces.

In 2004, when Giuliani wasn’t reminding the country of the importance of steadfast leadership in the face of adversity, he was ripping into the Democratic presidential nominee, Sen. John Kerry (D-Mass.), delivering a blistering attack on Kerry’s record with a combination of humor and slices to the jugular.

In Denver, Giuliani was tasked with communicating the GOP message that Obama and Democrats were “Not Ready in ’08.” It was a task well-suited to his star power and penchant for delivering the one line that will make it into the evening newscast.

Look for Giuliani to fulfill the same roll with his speech this week. He may not have the conservative bona fides to get himself on the GOP ticket, but when it comes to making the argument that the country is safer with Republicans at the helm of the ship, there is hardly a better performer under the spotlight.