What? Senators are elected, not appointed. They are not employees but officers. There are only a couple of ways to get rid of them ~ death(many hang around so long they die in office), or they get beat in a primary. A few retire ~ and most of those guys have taken leave of their senses long ago ~ their staff people run the office and tell them how to vote.
Senators can also be impeached, then tried, possibly removed from office .... and also ... prevented from ever holding another federal office.
Article II of the United States Constitution (Section 4) states that “The President, Vice President, and all civil Officers (Senators) of the United States shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other High Crimes and Misdemeanors.
William Blout (Senator from Tenn and signer of the Constitution) was impeached but the charges dismissed after being expelled from the Senate in 1797.