Dennis Prager has three reasons why Bush's Supreme Court nominee will be smeared:

"First, Democrats believe that conservatives by definition are bad people."
...
"A second reason Democrats and others on the Left use smear as a political weapon is to avoid challenging ideas and intellectual argument."
...
"Third, having been unable to persuade the American public to adopt most of its policies, the Left has increasingly relied on the courts to do what the political process will not do."

The whole thing is here.