Final answer:
The appointment of federal judges is most substantially influenced by partisanship. Judges appointed by a Democratic president tend to be more liberal, while those appointed by a Republican president tend to be more conservative.
Step-by-step explanation:
The appointment of federal judges is most substantially influenced by partisanship. Judges appointed by a Democratic president tend to be more liberal, while those appointed by a Republican president tend to be more conservative. Additionally, personal beliefs and political attitudes of the justices also play a role in their decision-making.