Scalia is a conservative and an originalist, yes, but his core ideology is, and has always been, legal clarity. In the short term, this might seem bad for Democrats. The upshot of the Booker decision, for example, is a muddled decision liberals can fall in love with. The Washington Post editorialized that the decision "did not produce an entirely coherent result from a legal scholar's point of view, but as a policy matter the outcome was the best that could have been expected."
That's OK, as far as it goes. But if the Supreme Court sees its mandate as making good policy decisions that are logically muddled, Democrats are sunk in the long term. Many of the court's future issues will come directly or indirectly through actions taken by the large Republican congressional majorities. With that likely docket, Democrats should attempt to seat a conservative court whose polestar is logic, as opposed to a court whose polestar is the White House.
With a Democratic president or a Democratic Senate, liberals could have afforded to demand someone preferable to Scalia. But they don't have either, and they might not for a while. Liberals can wait, evince impotent outrage when Bush nominates someone, then play their familiar role of the palooka, or they can make Scalia-flavored lemonade. One thing is certain: After a scuffle, Bush's nominee will end up on the court, regardless, and the left will have garnered nothing, unless it thinks in terms of bargains.
Having a moderate associate justice and Scalia as the new chief will sting from time to time. But there are plenty of vastly worse possibilities, and the White House is likely mulling them all over right now.