While most news channels focused on Sen. John McCain’s big night on Thursday, it was a battle of the B.O.s on Fox News.

Sen. Barack Obama, the Democratic presidential nominee, made a much-hyped appearance on “The O’Reilly Factor” to tangle with Bill O’Reilly. The talk-show host had been pushing so hard for an Obama visit, of course, his unrequited desire was a big topic at the secret meeting between Obama, NewsCorp head Rupert Murdoch and Fox News chief Roger Ailes.

Ever the showman, O’Reilly turned his new tape into a mini-series — only “Part 1″ aired Thursday (below) — and turned us commentators into previews for the remaining segments. But it was still good television.

Part 1 is about national security, with O’Reilly gingerly mugging as a salt-of-the-earth armchair general. He may pull down $9 million a year, but O’Reilly talks with the cadence and umbrage of any regular guy holding court at the bar — scrunching his face, interrupting, waving his hands and wondering whether Obama is tough enough to take on Iran.

He looked permanently perturbed with Obama’s answers. But he also offered his guest a few compliments. So Obama was correct to oppose the Iraq war as the “wrong battlefield,” O’Reilly observed, but wrong to oppose the surge. (Don’t even bother trying to square that.) Obama gave a good speech in Denver, O’Reilly conceded, but he still “bloviated” about Pakistan.

Obama was cool and cogent throughout, but O’Reilly’s audience presents demographic kryptonite to his political superpowers. Fox News viewers went for Bush by 9:1 last cycle, and prime-time shows — like The Factor — offer an even more conservative spin than daytime programming. Meanwhile, the average age of an O’Reilly viewer is 71. Obama has trouble with older Americans in general, but older Americans who voted for President George W. Bush and tune into O’Reilly? Even they may not be moved by this solid performance: