Monday morning's announcement by Rep. Bart Gordon, D-Tenn., that he would not seek re-election certainly stirred things up on Capitol Hill.
It's an exaggeration to say that the dam is breaking for House Democrats as incumbents in tough districts retire. But it's an understatement to say that four such members announcing their retirements in four weeks is a trickle.
One can understand the indigestion building in Democratic leadership offices in seeing Reps. Dennis Moore, D-Kan., John Tanner, D-Tenn., Brian Baird, D-Wash., and now Gordon all stepping down and opening up seats that will be difficult to defend. Add to that number the open seat created by Rep. Charlie Melancon's Senate run in Louisiana; it's a goner.
If a trend were to develop, it would start pretty much as this has so far.
Gordon's contest had been rated by the Cook Political Report as Likely Democratic until Nov. 19, when it was shifted to Lean Democrat. With his departure triggering an open seat, and with its Cook Partisan Voting Index at R+13 -- meaning that in presidential balloting it votes 13 percentage points more Republican than the nation as a whole -- it is now rated likely Republican.
Quite simply, not enough House Democratic members in tough districts have retired to cost the party its majority, but if a trend were to develop, it would start pretty much as this has so far.
Always being helpful, the National Republican Congressional Committee already has an effort designed to push a dozen or so wavering Democrats toward retirement decisions. On the other end, former Democratic Congressional Campaign Committee Chairman Martin Frost of Texas recently suggested that the Obama White House be willing to guarantee post-midterm election jobs to certain members if they opt to run for re-election and still lose.
Probably the best way to look at the Democrats' situation is to look at relative levels of security of each of their 435 seats compared to early June.
The Cook Political Report now has 174 seats in the Solid Democratic column; 44 others rated as Likely Democrat, meaning not yet but potentially competitive; and 23 more seats in the Lean Democratic column, meaning competitive.
There are 19 seats rated as Toss Up, in which neither party can claim a clear advantage. There are eight seats in the Lean Republican column, 16 in the Likely Republican group and 151 rated as Solidly Republican.
Put in a more understandable format, the current number of Solid and Likely Democratic seats is 218, coincidentally the barest possible majority.
That means that today, if Democrats just hold the seats they ought to be able to hold but lose 100 percent of the 50 competitive races, they would still hang onto their majority by an eyelash.
As a practical matter, no party has ever lost or won all of the competitive races, but the shrinkage we have seen lately in those Solid and Likely Democratic columns means that any more retirements in tough districts will be a problem for Democrats.
On June 2, there were 199 seats in the Solid Democratic column and 34 more in the Likely Democratic column, for a total of 233 in seats strongly favored for Democrats, 15 more than there are today. There were 21 seats in the Lean Democratic column and five seats for both parties in the Toss Up column.
On the Republican side, there were six seats in the Lean Republican column, 36 more in the Likely Republican column, and 134 in the Solid Republican column.
The field of endangered GOP seats is shrinking -- though Democrats do have legitimate chances with a handful -- while the number of Democratic seats in jeopardy has been expanding, in a trend that really accelerated over the summer.
As this column pointed out last week, when parties have tough years, they tend to lose a lot of open seats, though the range varies enormously.
Republicans lost 38 percent of their open seats in 2006, but Democrats lost a whopping 71 percent of their open seats 1994. The variable is the kind of open seats they are, whether they are safe or endangered districts.
But the more Democratic retirements in tough districts there are, the larger the GOP win percentage from that group is likely to be and the lower the percentage of Democratic incumbents that the GOP would have to knock off.
Ten percent of all Republican House incumbents running for re-election in 2006, a tough year for the GOP, lost, and 15 percent of all of the Democratic incumbents running in 1994 lost.
So this business of whether the GOP can or will capture a majority next year is based on a lot of moving parts, but one of the most critical is Democratic retirements in tough districts.
So far, only Illinois' filing deadline has passed. Over the next few months it will be critical to watch whether there will be a constant flow, if the dam breaks or it diminishes to a trickle. One thing is certain: The last month can't make Democrats feel any better.