The media is being polite. They are describing the collapse of the conservative control of the Republican Party as the "evolving of the Republican Party." What we are watching is really the death throes of conservative control of the Republicans, at least nationally. The fact that Specter has been forced to switch to the Democratic Party is just one more dead canary in the conservative coal mine.
The mechanism is, I suspect, that the conservatives have used the issue of "Who is more conservative?" as an election tool for years, much as they used the cry "Who lost China?" for years during the Cold War. They've used the cry "Who is more conservative?" since Reagan, in fact. The result is that they have elected the strongest right-wing extremists possible because they think that is the route to electoral success. It certainly mobilizes the base, especially after they allied with the evangelical religious conservatives of the Christian Coalition.
Suddenly (from their point of view) the public has realized the disastrous consequences of letting the conservatives run government and turned their back on conservatives. All except the strongest conservatives, in fact, have backed away. So have many of the evangelical conservatives. But as the moderates flake off from the Republican brand, the remaining conservatives still think this is just a bad patch and that conservatism is still the route to electoral success. Since things are going bad for them with the public, they are retreating to their strongest point - be more conservative. So the most extreme conservatives are being concentrated in the party and they are becoming more desperate, much as soldiers fighting a losing battle will.
The result is that extremists are running the party now, not the politicians. Limbaugh never compromises, and always goes for the most extreme position. So do the other talk show hosts, as do the extreme writers like Coulter. The good politicians are recognizing that won't work, but the base won't keep them in office if they don't adhere to the most extreme conservatism.
What we are watching is the death throes of the conservative movement, and they won't go quietly. They can't. Conservatism is inherently an extremist quasi-religion.
I'm at last enjoying the show. I suspect I am feeling a lot the way my parents did in 1944 when both the Germans and the Japanese were in retreat on all fronts. Neither fascist nation gave up, either. Both, if anything, became more extreme. The Kamikaze pilots are only one example of the extreme measures they took. So was the German enlisting of teenagers from the Hitler youth to defend Berlin and the German homeland behind the Rhine. So was the desperate German offensive of the Battle of the Bulge.
I do expect conservative extremism to get even worse in the near future, though. That will last until the talk show conservatives are dethroned as the effective leaders of the conservative movement.
At least, that's my current best guess.
Addendum 6:30 pm
Senate Minority Leader Mitch McConnell thinks that Arlen Specter's switch to the Democratic Party is a threat to the country.
I guess that as an extremist conservative McConnell can't distinguish between a threat to the Republican conservatives and a threat to America.