Can Supreme Court justices be impeached, or is the only check on them the appointment process? Can a SCOTUS justice be arrested for criminal acts?
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.
Of course congress can impeach SCOTUS judges. Better still, congress can eliminate any judges seat any time they want. Congress is the ultimate power in our government. Congress will not act because enough of the members of congress (house and senate) support the destruction of our constitutional republic and the implementation of socialist marxist tyranny. If the propaganda media told the citizens the truth of the situation, things would start changing. And this change has to be led by congress. It is the only government agency with the power to do so, absent a successful Article V Convention.
All federal judges can be impeached. One or two Supreme Court justices have been impeached, but none were ever convicted. Several lower court justices have been impeached and convicted.
Can a SCOTUS justice be arrested for criminal acts?
Yes.