Q:

What law grants life tenure to federal judges in the US?

In the United States, what law grants life tenure to federal judges? The Good Behaviour Clause of the Constitution says:

The Judges, both of the supreme and inferior Courts, shall hold their
  Offices during good Behaviour....

It is said that this was intended to mean that federal judges should have life tenure ... but I cannot find a reference for that (and in fact the link I posted never quote anything from the framers which would suggest that this clause was intended as a guarantee of life tenure to federal judges).
To me the clause would mean that they can stay in office until they show "good behaviour", that is, until and unless they are impeached.
Can Congress approve a statue which says that all federal judges will stay in Office for 5 years? If not, what provisions would that status violates and why? I don't interpret the Good Behaviour Clause as implying that judges will hold their offices for all their lives unless impeached. It only says that they stay in office until impeached, without specifying how long they stay in office.

A:

Your interpretation is correct.  The constitution says that judges stay in office "until and unless they are impeached."  That means that congress cannot impose a time limit on any judge's term of office.  If it did so, it would be contrary to the constitution.  The only grounds for removal are those to do with misbehavior.  Therefore, judges have life tenure.

