I don't subscribe to the view that I'm sure has been trotted out by conservatives on U.S. television--and that would be trotted out by liberals if it were President Kerry making the nomination--that the Senate's advise and consent role is essentially limited to the candidate's technical competence and lack of previous ethical lapses. There is a role for ideology, and for making sure that the Court doesn't go way off the deep end.
But it is the president's right to decide whose name to submit to the Senate, and you must realistically expect that the president's view of who would make a good justice will usually be affected by how compatible the nominee's jurisprudential beliefs are with the president's. Democratic legitimacy, too, suggests that the voters should have the ability, via their selection of a president, to affect who gets nominated to the Court.
Which leads me to this conclusion: I don't know a whole bunch about John Roberts, and it's legitimate for the Senate to investigate thoroughly before making a decision. But on the basis of what I personally know now, Roberts should be confirmed by a large margin. He's not who I would have picked, he's not who Schumer would have picked, and he's not who Kerry would have picked; but if I were a senator, I'd vote to confirm him if nothing turns up during the hearings, and I think Schumer and Kerry should do the same.
Here's another way to state it: I do not think Democrats have the right to insist on a nominee who is in some way "better" than Roberts. Who could they propose as an alternative, on the basis that Dubya cannot choose anyone more "conservative" than that person? I think Republicans were correct to realize that they couldn't demand anyone "better" than Breyer or Ginsburg, even though their base was longing to take revenge on someone for what happened to Robert Bork. And--with the critical caveat that this is based on what I know now and that there should be a deliberate process in the Senate rather than a rubber-stamping--I think the Democrats would be correct to realize that they can't insist that Bush appoint someone "better" than Roberts.
This is what I believe in principle. Whether it makes good politics is another question. I think it might, partly because it establishes a precedent for the next time a Democrat gets to make the pick, and partly because it makes it more credible if Democrats seriously oppose a truly objectionable second Bush Supreme Court nominee in the remainder of his term.
Maybe I'm wrong about the political strategy; but I think I'm right about the principle.