It's true. We have. Marc Thiessen writing in the Washington Post:

Just compare the records over the last three decades. Democrats have appointed four justices - Ruth Bader Ginsberg, Stephen G. Breyer, Elena Kagan and Sonia Sotomayor. All have been consistent liberals on the bench. Republicans, by contrast, have picked seven justices. Of Ronald Reagan's three appointees (Sandra Day O'Connor, Antonin Scalia and Anthony M. Kennedy) only Scalia has been a consistent conservative. George H.W. Bush appointed one solid conservative (Clarence Thomas) and one disastrous liberal (David Souter). With George W. Bush's appointments of Samuel A. Alito Jr. and Roberts, conservatives thought finally they had broken the mold and put two rock-ribbed conservatives on the bench - until last week, that is, when Roberts broke with the conservatives and cast the deciding vote to uphold the largest expansion of federal power in decades.

But why is that?

For one thing, the whole legal and political culture pushes the court to the left.  Conservatives are pariahs if they vote against the left on certain issues. But if they cross over vote with the left, they are hailed as statesmen. Just look the pre-emptive attacks on the Roberts Court when everyone thought it was about to strike down Obamacare - and contrast that with all the accolades Roberts is now receiving from his erstwhile critics.  Before the decision he was threatening to plunge the nation into a political crisis. Today he is praised for his "humility," "restraint," being "brave" and "judicial modesty." Meanwhile, many conservatives are twisting themselves in knots to defend or explain his vote. Not a chance the left would do the same if one of the court's liberals had voted to overturn Obamacare. There is no penalty for voting left, but there is for voting right.

Another factor is that liberal Supreme Court nominees can tell you precisely how they stand on key issues and still get confirmed. In her 1993 confirmation hearings, Ginsburg declared the right to abortion "central to a woman's life, to her dignity" and was confirmed 96 to 3. Breyer declared abortion a "basic right" and was confirmed 87-9. Imagine if a conservative nominee said the opposite? Their confirmation battle would be a nuclear war.

Liberal nominees can simply affirm liberal positions, while conservatives must speak cryptically in terms of their judicial philosophy. And as we saw last week, those philosophical statements do not necessarily indicate how they will vote on the bench.

I think Thiessen is on to something, although I think he slightly exaggerates about liberals simply stating the liberal position in their confirmation hearings. There are plenty of issues -- including gun rights, federalism, and judicial activism -- for which potential liberal justices all trim their sails a bit in order to get confirmed.

But he's spot on about how conservatives are grilled. I'm not sure, however, that any amount of direct answers from Roberts would have revealed his belief that loyalty to the Supreme Court as an institution trumps his loyalty to the Constitution. Besides, Roberts has been an otherwise reliable conservative vote since he was confirmed.

It is ironic the one decision he may be remembered for will be where he left the reservation to join the liberals on Obamacare.