The president's "argument" for her amounts to: Trust me. There is no reason to, for several reasons.
He has neither the inclination nor the ability to make sophisticated judgments about competing approaches to construing the Constitution. Few presidents acquire such abilities in the course of their pre-presidential careers, and this president particularly is not disposed to such reflections.
His argument seems a little arbitrary to me (vote against her confirmation because Bush didn't veto McCain-Feingold?), but it warms my heart to see dissention in the GOP ranks.
The Dubyaite counterstrike is even more amusing, noting that would-be Judge Harriet "happens to be a gun-toting evangelical who gives money to pro-life organizations." Whew, I feel better already.