Answer: to ensure that the justices are insulated from political pressure
We actually could have asked this question another way and the answer would have more or less gotten us to the same spot. That question could have been:
“Has any Supreme Court Justice ever been impeached?”
The answer to that one is “no“, but there was once a time where a justice was close, and it helps explain why justices now serve for life, or more likely until they retire.
You see, back in 1796, our nation’s first President appointed a man named Samuel Chase to the Supreme Court. While Washington thought him to be a good nonpartisan pick, Chase was anything but that. According to Mental Floss, Chase was “an openly partisan Federalist vehemently opposed to Thomas Jefferson’s Democratic-Republican policies, and he wasn’t afraid to say so, either in his role as a lower court judge or once he was appointed to the Supreme Court.” As a result, the House of Representatives voted to impeach Samuel Chase four years after the turn of the century. Keep in mind, Thomas Jefferson was now president at this time.
Despite Jefferson’s position in the oval office, the House of Representatives had a point and argued that Chase’s open political views did not fit the ideals of a nonpartisan group of judges. That being said, Chase “was acquitted of all counts in the Senate, and went on to serve as a Supreme Court justice until his death in 1811.” While that may not have been the outcome the House wanted, the lesson is what gives us the answer the original question above, which is why justices serve “for life”.
The whole point of allowing them to serve that long “is to shield the nation’s highest court from the kind of partisan fighting the Chase impeachment exemplified.” As History notes, “the Supreme Court grew into arguably the most powerful judicial body in the world in terms of its central place in the U.S. political order. In times of constitutional crisis, for better or worse, it always played a definitive role in resolving the great issues of the time.”
At the end of the day, our founding fathers decided that the only way to help this legislative body stay somewhat objective was by allowing never-ending term limits. The topic is still debated fiercely today.