[abclily]

Sentors have immunity from defamation lawsuits if they defame citizens from the senate floor?

[Bob]

Sentors have immunity from defamation lawsuits if they defame citizens from the senate floor?

Yes. they do. It's an aspect of the separation-of-powers concept and spelled out in the Constitution. Any holding of them to account must be done by the Congress itself. It can't be done by the Executive or Judicial branches of the government.

[nhoward14]

The Speech or Debate Clause (found in Article I, Section 6, Clause 1) in the United States Constitution states that members of both Houses of Congress

“...shall in all Cases, except Treason, Felony, and Breach of the Peace, be privileged from Arrest during their attendance at the Session of their Respective Houses, and in going to and from the same, and for any Speech or Debate in either House, they shall not be questioned in any other Place.”

[grey_whiskers]

It's the "Speech and Debate" clause of the Constitution.

From Wikipedia:

The Speech or Debate Clause (found in Article I, Section 6, Clause 1) is a clause in the United States Constitution which states that members of both Houses of Congress “ ...shall in all Cases, except Treason, Felony, and Breach of the Peace, be privileged from Arrest during their attendance at the Session of their Respective Houses, and in going to and from the same, and for any Speech or Debate in either House, they shall not be questioned in any other Place. ” Its intended purpose is to prevent a President or other officials of the Executive branch from having members arrested on a pretext to prevent them from voting a certain way or otherwise taking actions with which he or she might disagree.

Also see this case

Cheers!