That's definitely true for Republican presidents, but I don't recall any major defections by leftist judges to join with conservatives on the court on major decisions, at least not in the past few decades.
I think there are two major problems for conservatives:
1. Many Republicans still have the notion that a president should be able to put whoever they choose on the Supreme Court. We have never "Borked" a Dim nominee, but I can remember several Republican nominees that were withdrawn after leftist protests: Haynesworth, Carswell, Ginsburg (a man), and then Bork was voted down.
I might not be remembering all of them, but I do know Orin Hatch has bragged about how he got with Slick Willie to come with a fine nominee named Ruth Bader Ginsburg.
Because of the above, many of the most conservative potential nominees are never even nominated. We cull the best at the outset. The Dims don't.
2. Not all Republican presidents intended to nominate strict constructionist judges. Both Bushes put a liberal on the court, Souter and Roberts. Both were unknowns and the party just trusted the Bush president to nominate a conservative. Dims always seem to put a true leftist on the court. And Nixon and Ford were not conservatives on many issues, just as the Bushes were not conservative on many issues.
Also, look what the did to Clarence Thomas. The whole Anita Hill thing was so damn contrived.
Still, you forget one key player they have in their pocket that we do not: the media.
The driveby media—enemy of us all. They're still out there: plotting, planning and projecting. Don't’ forget what they did to Sarah, how they went after Newt (who fought back!!!), how George Stephenopolis baited Rick Santorum on birth control, their contrived War on Women and the Sandra Fluke kerfuffle, etc, etc, etc.
It just never stops with them.