As noted here and elsewhere, multiple retirements have been announced in the last 24 hours: Democratic Senators Byron Dorgan (ND) and Christopher Dodd (CT), plus Democratic Governor Bill Ritter (CO).

Adding in the other Senators planning to retire (three additional Democrats, six Republicans) — plus the D and R members of the House calling it quits (nine and 12, respectively, by last count) — this seems like one of the most extensive bipartisan movements of the past year.

But is that movement a flood or a trickle? Is it extraordinary or par for the course?

In the House, so far, it’s the latter. According to Chris Cillizza on Dec. 4, at the same point in the run up to the 2008 Congressional elections, there were also 21 announced House departures (albeit of a slightly different mix: five D’s and 16 R’s). Cillizza added that these sniffles could portend a more severe ailment:

There are 49 Democrats who sit in districts carried by Sen. John McCain (R-Ariz.) in 2008 and, among those, roughly a dozen and a half have held their seats for four or more terms.

It’s those folks — Reps. John Spratt (S.C.), Ike Skelton (Mo.) and Marion Berry (Ark.) to name three — to keep on your retirement watch list. If they go, an epidemic may well be declared.

We’ll see. In the meantime, an untested hypothesis keeps bouncing around in the back of my brain. Yes, some of these retirements are the result of known causes: For instance, Sen. Dodd. He miffed Connecticut voters when he moved with his family to Iowa in late 2007, to boost his presidential bid. Then, about a year later:

… it was reported that he had been included in a special VIP mortgage loan program by Countrywide CEO Angelo Mozilo. Dodd insisted he was unaware of his inclusion and he was cleared of any wrongdoing by the Senate Ethics Committee but the political damage was done.

Such cases notwithstanding, there seem to be several of these retirements with uncertain motives. For instance, Sen. Dorgan. His words, at least, suggest a very confident candidate:

This decision is not a reflection of any dissatisfaction with my work in the Senate, nor is it connected to a potential election contest next fall (frankly, I believe if I were to run for another term I would be reelected).

Of course, not everyone agrees with the Senator on his prospects for winning another term, and Republicans have their own theories:

“This development is indicative of the difficult environment and slumping approval ratings that Democrats face as a result of their out of control tax-and-spend agenda in Washington, and we fully intend to capitalize on this opportunity by continuing to recruit strong candidates who can win these seats in November,” said Brian Walsh, communications director at the National Republican Senatorial Committee.

Perhaps. But there could be more to it than that. My untested hypothesis: A potentially significant portion of these departing Members of Congress have decided to pursue other interests because, like many of the rest of us, they are just too damn sick and tired of the current, divisive, uncooperative, hysterical, attack-of-the-day political environment.

“Bah!,” you say. “If they can’t handle the heat, they should get out of the kitchen.”

I understand that sentiment. And to a certain degree, I agree with it. Debate is central to politics, and such debate is often, given the stakes, intense. No problem there. But that’s not what I’m talking about. I’m talking about an environment so disproportionately shrill, oversimplified, and mean-spirited that it’s no longer a debate. It’s a screaming match, 24 x 7.

My ultimate fear: We’re at or near the point where we’ll start to see more departures, and more of those departures will be prompted by extreme frustration with the counter-productive nature of the screaming match. Worse: Some of those who leave for this reason will be very good people who could have done a lot of good for this country, if they were presented with a more civil platform on which to constructively debate and address issues. In the end, I fear we’ll be left with nothing more than a cast of characters who enjoy screaming matches, and I’m just not sure we want those characters running this nation.