The only way a congressman can be removed is by impeachment (trial by the US Senate) or by expulsion (2/3 of the US House members). Only five expulsions have taken place in the history of the US, and three of those were during the Civil War.
No impeachment to remove a legislator. Each chamber is its own master when it comes to removing its own members.
Each House may determine the Rules of its Proceedings, punish its Members for disorderly Behavior, and, with the Concurrence of two-thirds, expel a Member.Impeachment (by the House) is akin to indictment, and removal of an impeached president of judge is at the whim of the Senate as it conducts an impeachment trial.