Historically, different U.S Courts of Appeal have varied in their ideological cast. The 9^th Circuit, which covers California and other western states, has long leaned liberal while the 5^th Circuit, which covers Texas, Louisiana, and Mississippi, has leaned conservative. But changes in the U.S. Senate approval process are giving President Trump the opportunity to bring a conservative tilt to all of the Courts of Appeal.

For many years, a judicial nominee’s home-state Senators played a major role in the appointment process. For example, Judiciary Committee chairs might block a President’s nominee to federal appellate (or trial) courts if either Senator from the judge’s home state didn’t sign off with their “blue slip.” Consultation with the home-state Senators also was routine. Hence, Presidents often chose judges acceptable to the home-state Senators. For California, that pushed nominees in a liberal direction, while for Mississippi, that took nominations in a more conservative direction.

But political polarization has led to the weakening of Senate prerogatives. And in the case of circuit court nominations, Senate Judiciary Committee Chair Charles Grassley no longer enforces the blue slip rule. As a result, President Trump has been able to appoint judges that were rejected by their home-state Senators and therefore to place strongly conservative judges on appellate courts throughout the country. Yesterday, for example, the Senate approved Judge Kenneth Lee to the 9^th Circuit over the objections of California Senators Dianne Feinstein and Kamala Harris. Last week, the Senate approved two judges to the 2^nd Circuit over the objections of New York Senators Chuck Schumer and Kirsten Gillibrand.

As Trump appoints more judges—and he’s already filled more than 20 percent of the 179 appellate court seats with his 40 appointments—his imprint will grow, and the different Courts of Appeal will move together in a more conservative direction.

Of course, both sides can play this game. If Democratic Judiciary chairs follow Grassley’s lead when voting on nominees by Democratic Presidents, then we will see the different Courts of Appeal move in a a more liberal direction across the board. Either way, it’s not a good sign. We’re better off with a mix of conservative and liberal judges or courts rather than a skew in either direction.