If they can delay Alito's hearings, it implies Bush is weak...and they can concentrate on their pet project: driving him out of office. A speedy confirmation would emphasize Bush's strength and take headlines away from the Wilson nonsense. This is all about '06 and '08.
("Denny Crane: Gun Control? For Communists. She's a liberal. Can't hunt.")
Whether you want to hear it or not, Bush is weak. A lame duck president with many opposed to the war, suffering from controversy about the Plame affair, the rising energy crisis, as well as other issues.
But none of the above should influence or derail the confirmation.