Read this article by David Berke @berkeslaw firstname.lastname@example.org berkeslaw.net
At the start of each new Congress, the entire House of Representatives and one-third of the Senate takes the Oath of Office. This solemn act dates back to the First Congress in 1789. The current oath, however, is the product of the Civil-War era members of Congress intent on ensnaring traitors. The oath is not voluntary. It is universal. It binds every representative, regardless of party affiliation or political philosophy. Every punitive procedure such as impeachment, censure, contempt and the like, relates to some violation of this Oath of Office:
"I do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion; and that I will well and faithfully discharge the duties of the office on which I am about to enter: So help me God."