Who was the only Supreme Court Justice ever impeached?

Answer: Samuel Chase. This Washington Post story has the interesting story, which shows that judges shouldn't always just side with prosecutors:

Samuel Chase was a frequent subject of the rumor mill for his entire life. As a young lawyer in Annapolis, Md., in the 1760s, he was expelled from a debating society for “extremely irregular and indecent” behavior. He was also an early critic of the Stamp Act and headed up Anne Arundel County’s chapter of the Sons of Liberty.

His height and broadness added to his gruff and intimidating personality. He also had a reddish-brown complexion, earning him the nickname “Old Bacon Face” — which some might consider its own impeachable offense.

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President George Washington nominated Chase to the Supreme Court in 1796. At the time, though, the highest court in the land had little to do, so justices still served on lower courts.

And those lower courts are where Chase’s problems arose.

While presiding over the 1800 sedition trial of Thomas Cooper, Chase railed against Cooper during his instructions to the jury, seeming to act more as a prosecutor than a judge.

Before a treason trial in Philadelphia, he showed defense attorneys his opinion before the trial had even taken place. He later sentenced the man to death. (President John Adams pardoned him.)

At a sedition trial in Richmond, he sat a juror who said he had already made up his mind that the defendant was guilty.

And while presiding over a grand jury in Delaware, Chase angrily refused to dismiss a grand jury after it declined to charge a man with sedition.

But all of that is background to why he ended up getting impeached:

Once they had the reins of power, the Democratic Republicans overturned a law that had created lower courts in a bid to limit the power of Federalist judges installed by Adams.

But that didn’t stop Chase. In 1803, before a Baltimore jury, Chase denounced the Democratic Republicans for overturning the law.

When Jefferson found out about it, he sent a letter to a congressman friend strongly suggesting that — cough cough, hint hint — only Congress could do something about Chase.

The next year, the House voted 73-32 to impeach him, charging that he “tend[ed] to prostitute the high judicial character with which he was invested.”

The Senate trial took place in February 1805. Over 10 days, senators heard from more than 50 witnesses, according to Rehnquist. Chase maintained that he could not be impeached for poor judgment, but only indictable offenses.

Two-thirds majorities were needed to convict on each of the eight articles of impeachment. If the votes had gone strictly down party lines, Democratic Republicans would have had more than enough; at the time, they dominated the Senate 25 to nine, according to the Senate Historical Office.
But that isn’t how the votes went. Though majorities found Chase guilty on three of the eight articles, none passed the two-thirds threshold.

Old Bacon Face had dodged the frying pan.

And a precedent had been set, Rehnquist said, that “a judge’s judicial acts may not serve as a basis for impeachment.”