He’s not reviving the Bull Moose Party just yet, but McCain’s obsession with TR is beginning to have an impact at the Capitol. McCain once had a reputation as a bully, the kind of senator who was better at lecturing colleagues than at pulling them together. No more. Modeling himself after his idol–the most skillful reformer who ever happened into the Oval Office–McCain has emerged as the leader of moderates in both parties, pushing campaign reform in both chambers and introducing compromise bills on gun control and a patient’s bill of rights, which hits the floor this week.

Some Republicans worry that McCain will take this TR thing to its extreme–bolting the party in 2004 to challenge a GOP president, as Roosevelt did when he founded the Bull Moose Party in 1912 to dethrone William Howard Taft. The speculation grew so rampant recently that McCain summoned his advisers to his office and told them not to discuss the possibility of an independent campaign, with him or with each other. “Have any of us fantasized about it? Sure,” says Mark Salter, McCain’s chief of staff. “Have any of us really looked into it or prepared for it? No. Because none of us knows if he would do it.”

Still, McCain’s allies say it’s their job to keep McCain’s options open, just in case. Quietly, they’ve assembled a network of groups to challenge GOP orthodoxy and lay the ideological groundwork for a possible third party. One, the Project for Conservative Reform at the right-leaning Hudson Institute, uses TR’s bull moose as its emblem and addresses policy statements to the “Moose-keteers.” The project’s director, McCain adviser Marshall Wittmann, routinely skewers George W. Bush for his dependence on corporate money, just as Roosevelt’s followers targeted machine politicians a century earlier. None of this is lost on the White House. Since the GOP lost control of the Senate in May, Bush aides have been on the lookout for any sign of a McCain defection. Chuck Hagel, the GOP Nebraska senator who’s close to both McCain and Bush, was standing in a cornfield recently when he got a frantic call from a senior Bush aide on his mobile phone. The White House had heard that McCain was hosting Democrats at his Sedona ranch. Was he going independent? “Well, I just talked to him two hours ago,” Hagel said. “How much trouble can a guy get into in two hours?” Hagel dialed Sedona, and before he could speak he heard McCain’s voice pick up with the words: “No, I am not changing parties.” The two shared a good laugh.

McCain says he intends to remain a loyal Republican–and to pursue his own reform agenda. Coming soon: a proposal for some kind of ambitious national-service program, part of his ongoing effort to reach out to cynical independents and drag the party toward the center on domestic issues. And if it won’t go? “There is a growing vacuum out there,” McCain says. “Unless the two parties move to fill that vacuum, you will see the rise of independent candidates.”

What McCain doesn’t say, and surely knows, is that, at least for the moment, he’s the only serious political figure who can fill the void. A poll conducted last month by his pollster, John Zogby, found McCain’s approval rating at a remarkable 70 percent among independents. “To many voters, he’s the last honest man in America,” Zogby says. McCain has missed airline flights because people mob him in airports; at a Georgetown basketball game, he received a thunderous ovation–except from the corporate boxes, where there were scattered boos. McCain basked in both. For him, as TR might have put it, the moment was just bully.