There have been many contenders throughout US history, but I do believe the she is the absolutely dumbest Congressperson ever, period. And, she gets bonus points for being crazy AND vocal about it.
She has competition from Barbara Boxer on that front.
And Nancy Pelosi just for her "have to pass the bill to see what's in it" statement.
And the guy that thought that Guam would capsize.
And that woman that thought the US sent men to Mars to plant the flag.