BUT WHAT IF MY OPPONENTS ARE CRAZY?…. James Joyner, a conservative I find to be both thoughtful and reasonable, had an item today reminding political observers not to assume “that your opponents are crazy.”

James concedes that there are “a lot of angry nuts on my side of the aisle,” but adds that there’s “plenty of crazy to go around.” He points to some liberal conspiracy theories we heard during the Bush years, and suggests it would unfair to “judge the left by the whackos.”

That sounds a like an entirely sensible approach to modern politics. But I think James is making an important mistake, which I hear/see frequently, especially from major media outlets. The conventional wisdom is that the left has some nutjobs, and the right has some nutjobs, but this is unrelated to political mainstream of both major political parties. Wacky liberals said ridiculous things under Bush; wacky conservatives are saying ridiculous things now. Move along; nothing to see here.

Kevin Drum noted some of the flaws in this.

Now, obviously there’s some truth to this, but there are a couple of things that have struck me about the recent surge in conservative nutballs. First: there’s just a whole lot of them. The Diebold folks couldn’t even get a hearing at Daily Kos, let alone anywhere more mainstream. The 9/11 truthers have always been a tiny band. And most of the people who believed Bush “knew about 9/11” just thought he had been warned something was coming down the pike. There was never more than a trivial handful who thought he literally knew the details and deliberately let the plot go forward.

Second: the conservative lunatic brigade appeared so goddamn fast. It’s true that some precincts on the left went nuts over Bush, but anti-Bush venom didn’t really start to steamroll until late 2002 when he was making the case for war against Iraq. Nobody drew BusHitler signs after he signed NCLB or called him a war criminal for signing a tax cut. It took something really big to create a substantial cadre of big league Bush haters.

Conversely, the conservatives who think Obama is a socialist, or think Obama was born in Kenya, or think healthcare reform is going to kill your grandma, or think Obama is going to take all your guns away — well, that stuff started up approximately on January 21st, if not before. And it’s not just a weird 1% fringe. There’s a lot of conservatives who believe this stuff. And there wasn’t any precipitating cause other than the fact of Obama’s election in the first place.

I agree wholeheartedly with all of this, but I’d add something else — the mainstreaming of Republican radicalism. In the Bush/Cheney years, the Democratic establishment and prominent center-left outlets wanted nothing to do with 9/11 truthers and/or Diebold folks. It was unheard of to see a Democratic member of Congress call Bush/Cheney “fascists,” or encourage the Democratic Party to emulate the Taliban.

Conversely, the line between fringe right-wing stupidity and the Republican/conservative mainstream has all but disappeared. Vile nonsense may start on a Freeper thread, but it won’t stop there — the same garbage is invariably found on major far-right blogs (Malkin, RedState), prominent conservative magazines and newspapers (National Review, Weekly Standard, WSJ), talk-radio shows with huge audiences, Fox News, and far too often from elected Republican officials.

Whereas Dems kept the fringe at arm’s length, Republicans embrace the fringe with both arms. Both sides have nutjobs; only one side thinks their nutjobs are sane.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.