THE NAME Nathan Deal does not ring many bells outside the 9th Congressional District of Georgia, a swath of farming communities and mill towns that cuts across the northern part of the state from the South Carolina border to the Alabama line.
While less prominent than the two Democratic senators, Richard Shelby of Alabama and Ben Nighthorse Campbell of Colorado, who recently switched parties, Mr. Deal's defection is in some ways a more ominous development.
Senator Shelby flirted with the GOP for years and Senator Campbell was regarded as a flake. Mr. Deal, by contrast, was the author of a welfare-cutting plan that had won the support of even the most liberal Democrats.
He was praised conspicuously by his Democratic colleagues, and then, like a longtime employee who announces he's quitting at his own testimonial dinner, Deal walked out of the party and joined the arch-rival.
Mr. Deal's defection carries an ominous portent for Democrats in how it changed the composition of Georgia's House delegation: Of the 11 members, all of the Republicans (eight) are white and all of the Democrats (three) are black.
There is a pervasive fear among Democrats that this is just the beginning of a hemorrhage that could culminate in the secession of as many as 23 conservative Democrats.
While it will probably not reach those calamitous proportions, it seems likely that Mr. Deal has broken the taboo and that others will reach the conclusion that the GOP franchise is worth more in their districts than the Democratic.
Dixie Democrats with itchy feet are nothing new. Since 1964, they have made rebellious noises and complained sullenly about the excessively liberal stands of the national party, especially on civil-rights questions, but few actually jumped ship.
Those who did usually met with little success as Republicans. For every Sen. Phil Gramm, R-Texas, there were half a dozen who failed as Republican vote-getters. Their districts may have given majorities to Republican presidential candidates, but all local offices were in the hands of Democrats.
Party allegiance was genetically encoded in these voters, who would routinely turn their backs on George McGovern and Michael Dukakis but vote the straight Democratic line from sheriff on up to congressman. That ossified Democratic localism has now begun to disintegrate among white Southern voters.
Being able to vote pretty much as they pleased was one factor that held disenchanted conservative Democrats within the party.
Some, like Texas' Ralph Hall, support the party line on less than half of all House votes and suffer no penalty. Some were even favored with committee chairmanships.
Perhaps the most compelling argument Democratic congressional leaders would use on potential strays was that they would suffer a traumatic loss of influence moving from the majority to the minority party.
That argument expired last Nov. 8. Indeed, it is House Speaker Newt Gingrich, R-Ga., who now has the coffer full of blandishments to lure Democrats across the aisle.
The most potent counter-argument that Democratic leaders can muster now is that conservatives are celebrated rarities in the Democratic Caucus but would be nothing more than part of the common herd on the GOP side.
What should trouble the Democrats most is the prospect of an avalanche of defections polarizing Southern politics along racial lines, so that being Republican and white and Democrat and black become conterminous.
That kind of stark division of the electorate would deprive the Democrats of any hope of expanding their power in the South outside the 23 so-called minority districts that are virtually guaranteed to elect black Democrats.
There are 130-plus House seats in the vast stretch between the Potomac and the Rio Grande. A toehold of 23 is not much for a party that once claimed sovereignty over the Solid South.
Ross K. Baker is a professor of political science at Rutgers University.