In the right corner, Congressman Paul Ryan. In the left corner, Nation editor Katrina vanden Heuvel.
The result: a vicious knockout for Ryan. (The exchange starts at about 3:27.)
Towards the end, you even see MSNBC's referee Carlos Watson try to step in and stop the fight, but Ryan will have none of it. He gets in a few more finishing shots, and she's down for the count.