Unlike these past relationships, however, the most dynamic duo in Washington today crosses party lines. Old-school realist Richard Lugar, the five-term Republican senator from Indiana, has embraced new-school realist and rising star Barack Obama, the junior Democratic senator from Illinois. The relationship is admiring. “I very much feel like the novice and pupil,” Obama has said of Lugar. And it’s warm. Lugar praises Obama’s “strong voice and creativity” and calls him “my good friend.” In short, the two agree on much and seem to genuinely like each other. Rather unusual in hyper-partisan Washington, these days.

Like most friendships inside the Beltway, this one involves some mix of affection and career advancement. But it is also built, rather charmingly, on shared wonkish interests. By most accounts, Obama and Lugar’s working relationship began with nukes. On the campaign trail in 2004, Obama spoke passionately about the dangers of loose nukes and the legacy of the Nunn-Lugar nonproliferation program, a framework created by a 1991 law to provide the former Soviet republics assistance in securing and deactivating nuclear weapons. Lugar took note, as “nonproliferation” is about as common a campaign sound-bite for aspiring senators as “exchange-rate policy” or “export-import bank oversight.” Soon after Obama won the election, the two men exchanged phone calls. Lugar, who chairs the Senate Foreign Relations Committee, suggested that the younger senator aim for a seat on the committee; Obama did, successfully.

The two men grew closer in August of 2005, when Obama joined Lugar on a tour of Russia and Eastern Europe to inspect weapons facilities, a trip that Lugar makes annually. For the younger senator, it was a chance to see first-hand the situation that had long unsettled the older statesman. In Kiev, they visited a pathogen laboratory, an unsecured nondescript downtown building, where the senators were shown a storage unit resembling a mini-refrigerator that contained vast rows of test tubes. Some tubes held anthrax; others, the plague. As Obama has recounted the story, “At this point I turned around and said ‘Hey, where’s Lugar? Doesn’t he want to see this?’” But the older senator was standing in the back of the room, nonchalantly. “Been there, done that,” Lugar said.

The two men were also detained for several hours in the Russian town of Perm, when local border officials suddenly demanded to search the senators’ plane. After some angry phone calls from Washington, the plane was released, but, Lugar noted, “it makes you wonder who really is running the country.”

Most important, though, may have been the timing of the senators’ visit to Ukraine and Azerbaijan. Russia had chosen that moment to escalate a dispute with Ukraine over national gas by cutting off the pipeline that supplies Russian gas to Ukraine and Germany, threatening the economy of much of Western Europe. Meanwhile Azerbaijan’s economy was set to go on steroids with the completion of its own gas pipeline to the West. The trip focused Obama’s attention on the tight link between energy resources and national securitya longtime concern of Lugar’s.

Something else unfamiliar happened on the tripor at least something that rarely happens in the United States: Lugar overshadowed Obama. In Russia, where Lugar has been a regular visitor for the past 15 years, the senior senator from Indiana received generous media coverage and attention from political leaders, while the junior senator from Illinois sometimes went unrecognized. “If anybody has ever accompanied Senator Lugar on a trip,” Obama would later joke to an audience at the Council on Foreign Relations, “you know that he is a rock star wherever he goes.”

After returning to Washington, Lugar and Obama co-sponsored legislation to update the Nunn-Lugar program. The resulting law, which expands the nonproliferation program for nuclear arms to conventional weapons and WMDs, is called the Lugar-Obama Act, a name that “virtually rolls off the tongue,” in the approving words of Scripps-Howard columnist Martin Schram. This March, Lugar and Obama introduced the American Fuels Act of 2006, an ambitious bill that would drive investment in biomass ethanol. And, in late July, the two senators were among the co-sponsors of a bill to raise automobile fuel-efficiency standards.

Of course, friendships across the Senate aisle aren’t so unusual. (Ted Kennedy once composed a serenade for his teetotalling buddy Orrin Hatch: “Wherever I go/ I know Orrin goes/ no fits, no fights, no feuds, no egos/ amigos/ together.”) But bipartisanship is uncommon in mentor relationships. One might expect Obama, for example, to sidle up to someone like John Kerry, or five-term Michigan Democrat Carl Levin. And Lugar might be expected to take a young Republican whippersnapper under his wing, both in the name of party loyalty and of molding Republicans of the future.

Still, if Obama wants to see any legislation with his name on it pass, then having a Republican teammate makes more sense. Unlike many Democrats in Congress, Lugar has the ability to get a few things done. And, if Lugar is looking to secure his legacy by passing on his moderate, substantive foreign-policy vision to someone who’s open-minded, sensible, respectful, and destined for leadership, Obama’s not a bad choice. To put it differently, what current Republican freshman would fit the bill?

Indeed, in a political atmosphere where conservatism increasingly appears to be leaving the realm of reason altogether, moderate Republican holdouts like Lugar begin to have more in common with characters across the aisle. While the GOP, led by the White House, has spent most of the decade trying to dismiss global warming as a liberal hoax, Lugar has since the late 1990s been calling for action on the problem and refers to the impasse over the issue as one that “sometimes leaves the science and becomes almost theological.”

One reason Lugar can afford to speak his mind is that, at 74 years old, any ambitions for higher office are now behind him. In 1996, Lugar made a bid for the GOP presidential nomination that didn’t go far, and he hasn’t run since. Still, the past comes up once in a while. Recently, a Russian newspaper announcing Lugar’s visit ran a picture from the 1996 campaign. According to The Chicago Tribune, the campaign photo prompted someone to ask Lugar if he would consider running for president again. The old lion shook his head and passed the torch. “That’s for Barack,” he said.