I missed this article – Originalists, Politics, and Criminal Law on the Rehnquist Court by Rachel Barkow – when it came out, but I thought this part of the abstract was interesting:

By reviewing all of the Rehnquist Court’s criminal opinions in argued cases during the ten-year period from the October 1994 Term through the 2003 Term, this Article shows that the Justices’ votes in criminal cases do not fit neatly into the attitudinal model. [Mike Rappaport insertion: the attitudinal model holds that the votes of the Justices are based on their political views, not the law.]  While a review of those cases confirms the conventional view that the Court’s liberal bloc voted for criminal defendants more frequently than the Court’s conservatives in non-unanimous cases, the more interesting pattern is the variation among the Court’s conservatives in non-capital criminal cases in which the five conservatives disagreed among themselves. In the fifty-five non-capital criminal cases in which the Court’s conservatives did not vote as a bloc, Justices O’Connor, Scalia, and Kennedy each voted for the defendant twenty-four times, Justice Thomas voted for the defendant in eighteen cases, and Chief Justice Rehnquist in fourteen cases. In several of the most important constitutional decisions of that period, including but not limited to the jury cases, the conservative originalists voted for defendants while the pragmatist conservatives ruled for the government. The jury cases are therefore part of a larger pattern that reveals the relationship between originalism, politics, and criminal law to be far more complicated than is commonly believed.

The question whether the justices vote based on their ideology or on the law is an interesting one.  I tend to have mixed views on this matter.  On the one hand, I believe that justices do, as a general matter, vote based on ideology in cases where they care about the outcomes.  That, of course, does not mean the opinions read that way, but in my view the underlying cause of their votes is ideology.

That said, I believe that the justices will vote based on a view of the law if they are strongly committed to that legal view.  Thus, Justices Scalia and Thomas are committed originalists and therefore will often vote based on their view of the original meaning, even if it leads them to vote in favor of specific results which they would not otherwise support.  In the block of cases review in this article, Justices Scalia and Thomas supported the original meaning of (1) the right to a jury trial in a criminal case and (2) the right to confront witnesses, and this original meaning often provided more protection to criminal defendants than court precedent did.  As a result, these justices ended up voting for criminal defendants more often than their ideologies would otherwise have suggested.