The Democrats will get most of what they want because Republicans don't fight back. And 51 Democrats in the Senate can always count on RINOs like Specter, Graham, McCain, Hagel, Snowe, Collins, and Warner to side with them on important issues like judges, Patriot Act, military prisons, taxes.
And all the bad things that happen, through the willing help of the MSM, will be blamed on the Republicans.
"Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached." -Manuel II Paleologus
I doubt that it will even get to be as bad as you predict, and remember that McCain and Hagel are still running for the '08 GOP Presidency and want the majority of conservative votes. Also, Warner's Senate seat is up in '08, and if he decides to run again, then he will be wanting the majority of the Virginia conservative votes in both the Republican Primary and during the general election.