Halfway through Chris Matthews’s mugging of Republican National Committee chair Reince Priebus yesterday on MSNBC, I had a flashback. It was to the moment almost eight years when Jon Stewart so humiliated Crossfire hosts Paul Begala and Tucker Carlson that he ultimately forced the show off the air. What the two moments have in common is this: a major media figure refused to play by the rules.

The rules, unwritten but well understood by people in the interwoven media and political world, is that it’s all in good fun. Liberal and conservative talking heads perform their disagreements for the camera but don’t question their opponents’ basic decency. Journalists ask politicians questions politicians don’t want to be asked, but then, when offered an evasive answer or two, smile and move on. It’s like Olympic fencing. When your blade strikes the other competitor, it beeps, signifying that you’ve won a point. But it doesn’t cut.

Yesterday morning, Chris Matthews decided not to play by those rules. Matthews is an unusual TV pundit for two reasons. First, he’s a moralist, and not always in predictable ways. In the late 1990s, he was furious about Bill Clinton’s sex scandals. Now he’s enraged by the GOP’s efforts to make President Obama seem pro-welfare (read: pro-black) and un-American. Second, he’s a student of American political history, and thus refuses to be willfully naïve about the pedigree that race-soaked issues like welfare have in presidential campaigns.

Like Begala and Carlson in 2004, Priebus was unprepared to deal with Matthews’s brazen sincerity. “You got your monologue in, so congratulations,” he responded, thus implying that Matthews was just performing like everyone else. Constrained by his own role as chief Republican flack from really grappling with Matthews’s charge, Priebus uttered some well-worn and barely relevant talking points about Obama’s misdeeds. Then he simply demanded that the conversation end. “I’m not going to get into a shouting match with Chris, so you guys can move on,” he told host Joe Scarborough, essentially asking him to reimpose the rules that usually govern such discussions on air. It reminded me of Carlson’s plea to Stewart: “I thought you were going to be funny. Be funny.” Essentially: get back in character. Don’t you know we’re all just playing a game here?

I have absolutely no idea what Reince Priebus really thinks about the Romney campaign’s apparent decision to make the president’s blackness and supposed foreignness an issue. My guess is that he doesn’t think about it at all: he’s a professional. And he assumed Chris Matthews was too. To Priebus’s horror, Matthews instead decided to be a human being.