Social conservative leader James Dobson decried the compromise as a loss for the Republicans. But undermining the filibuster is certainly more of a gain than a defeat for the GOP.
From Dobson's statement:
This Senate agreement represents a complete bailout and betrayal by a cabal of Republicans and a great victory for united Democrats...
We are grateful to Majority Leader Frist for courageously fighting to defend the vital principle of basic fairness. That principle has now gone down to defeat. We share the disappointment, outrage and sense of abandonment felt by millions of conservative Americans who helped put Republicans in power last November. I am certain that these voters will remember both Democrats and Republicans who betrayed their trust.
Look at the opening of the second paragraph in particular: Dobson has just definitively ended any remaining speculation as to whether he and his supporters ally themselves with individuals or with parties. They support Bush, they support Frist, they do not support Republicans at large. But now that Frist's 2008 campaign is essentially over before it began, they lack a future candidate -- and more, are unlikely, after having been burned in this battle, to attach themselves to another. They're most likely to simply stay home.
Corn may well be right to say that the Dems lost when it comes to the filibuster itself. But that certainly doesn't mean the Republicans won. They may have the filibuster, but they just lost the 3 million or so voters that handed them the election.