Now Mr. Graham is playing an even higher-profile variant of that role, as the Senate’s foremost expert on military law in the midst of the emotional debate over what rights to provide to terror suspects.
A former military lawyer who is also a reserve judge on the Air Force Court of Criminal Appeals, his influence is shaping up to be pivotal in forming the Congressional response to the Supreme Court ruling striking down the White House’s plan for bringing terror detainees to trial.
Mr. Graham advocates using the existing court-martial system as the basis for trying suspects, a position that has drawn fire from many other Republicans. They say it could cripple the government’s ability to protect the nation by giving detainees too many rights and making it harder to use highly classified intelligence against them.
But drawing on his own experience and a deep personal loyalty to the military justice system, Mr. Graham is working across party lines to try to assemble a consensus for his approach, saying it is sound legally and in terms of national security.
His views are shaped not only by his understanding of the law, but also by his respect for an institution he credits with changing his life, by shaping his career and allowing him to support his 13-year-old sister after his parents died when he was in college. His belief in the integrity of the military code has repeatedly led him to resist the White House when it comes to defining the treatment of people accused of being terrorists.
Last year, against the wishes of the Bush administration, he was one of the key forces in helping pass a ban on torture. Last week, he raised questions about the judicial nomination of William J. Haynes II, the Pentagon general counsel who helped write a memorandum that narrowly defined torture only as treatment that causes pain similar to death or major organ failure.
While some other Republicans argue that terrorists do not deserve legal or human rights, Mr. Graham has insisted that only a system grounded in the fundamental rights of the military code and the Geneva conventions will affirm the reputation of the United States abroad and protect American troops when they are captured by enemies.
“What I’m trying to do with my time in the Senate during this whole debate we’re having is to remind the Senate that the rules we set up speak more about us than it does the enemy,” Mr. Graham said in an interview. “The enemy has no rules. They don’t give people trials, they summarily execute them and they’re brutal, inhuman creatures. But when we capture one of them, what we do is about us, not about them.
“Do they deserve, the bad ones, all the rights that are afforded? No. But are we required to do it because of what we believe? Yes.”
Administration lawyers have argued for Congress simply to ratify the tribunals that the Supreme Court ruled that the president could not set up on his own.
Mr. Graham has fought back in his hyperkinetic, folksy way. Challenging the lawyers this week, he bounced in his chair, rolled his eyes, shook his head and raised his voice, warning at one point that if they pushed the president’s approach, “It’s going to be a long hot summer.”
“I’m a big fan of the Geneva Conventions,” he declared.
At a hearing last week, Mr. Graham backed up Senator Hillary Rodham Clinton, Democrat of New York, as she prodded military lawyers to refute the claim of some Republicans that providing legal rights to terror suspects was tantamount to setting them free.
“Isn’t it correct,” Mr. Graham asked the panel, after making a polite interruption, “that you could be acquitted in a military commission and still be held as an enemy combatant — even if you’re acquitted?”
Nodding at Mrs. Clinton, he explained: “It goes to your point. You’re absolutely right.”
In an interview later, Mrs. Clinton called Mr. Graham’s position “a perfect example of when someone’s experience can be used to inform an issue.”
