Why a New Nomination is Necessary:
Marty Lederman weighs in at SCOTUSBlog. Sounds right to me.
Tom from MD (mail):
I suppose if they wanted to, the Senate could comfirm Roberts as an Associate Justice, thereby getting rid of O'Conner, and then raise him to Chief Justice.

But given that it is in the Republicans' best interest to have Roberts replace Renquist, and thereby maintain a stronger conservative majority (5-3 instead of 4-3) until they can replace O'Conner, this isn't going to happen.
9.5.2005 2:13pm
Stevethepatentguy (mail) (www):
Tom strikes at the heart of the matter. The nomination os Roberts as Chief Justice is in addition to the nomination an Associate Justice, replacing O'Connor. A subsequent nomination will come to replace Rehnquist. The subsequent nomination will come fast with a tight timeline to bring the Court up to nine.

The S.Ct can and will operate with less than 9 Justices (6 form a quorum, 28 USC 1). It is politically expedient to replace O'Connor quickly with Roberts who is (I believe) much more conservative than O'Connor and then replace Rehnquist with a justice having "Rehnquist mindset", if that can be determined.
9.5.2005 2:25pm