What is wrong with what Senator Elizabeth Warren quoted according to the Senate rule 19?

http://www.cnn.com/2017/02/07/politics/elizabeth-warren-silenced/
“Senate Majority Leader Mitch McConnell defended invoking Rule 19, a rarely used chamber regulation that prohibits senators from impugning each other.”
_*“im·pugn verb, dispute the truth, validity, or honesty of (a statement or motive); call into question. “the father does not impugn her capacity as a good mother” synonyms: call into question, challenge, question, dispute, query, take issue with
“are you impugning my judgment?”*_
https://www.google.ca/?gfe_rd=cr&ei=H8WbWN2TDqOi8wfc8LaIDw&gws_rd=ssl#q=impugning+meaning