Why do some politicians block Supreme Court nominations? New research suggests their votes depend partly on the departing justice's ideology. The analysis finds that U.S. senators evaluate nominees along two main ideological axes: their own distance from the nominee and the potential shift in the court's median vote after confirmation. Crucially, this study reveals an additional factor influencing opposition: senators also react to how much a nominee contrasts ideologically with the departing justice.

Researchers examined data from 1968-2006 to understand these dynamics — specifically looking at votes against nominees and comparing them to the ideology of the retiring justice. Their findings show that ideological proximity to the outgoing judge plays a significant role in determining how senators cast their ballots against certain types of nominees.

This suggests more complex motivations behind judicial appointments than previously understood, highlighting factors beyond simple partisanship or alignment with the president's choices.