If inability to read the Constitution is not an impeachable offense it should be.
Article II
The President, Vice President, and all civil officers of the United States, shall be removed from office on impeachment for, and conviction of, treason, bribery, or other high crimes and misdemeanors.
Article III
The judges, both of the supreme and inferior courts, shall hold their offices during good behaviour.
Vastly different requirements.
I don't think he fears impeachment.