Found this idea, on http://corner.nationalreview.com/05_07_17_corner-archive.asp#070074
(Warning: extreme right wing site. Make sure to clean aura afterwards.)
WILD, CRAZY SPECULATION [Jpod]
What if...Bush chose Roberts because Rhenquist recommended him, since Roberts had been his clerk? And what if...there was some quid pro quo, like maybe waiting to step down until after Roberts was confirmed so that the Dems would be under pressure to confirm the next nominee because the Court will be in session?
This could explain a lot. It also explains why Bush would feel comfortable pushing in Roberts in such a transparent attempt to distract from Rove - the plan's in the bag, for someone *really* conservative to be nominated after Roberts gets in.
And in a possible larger plan, Bolton's nomination could also be waiting until Rehnquists's replacement triggers the Nuclear Option. If it goes down and the Democrats lose, Bolton can just be shoved through the GOP rubber-stamp mill before lunch.