The President addressed a joint session of Congress. The House is one branch, and the Senate is another.
In the early 1900s, women who asked for equality, were treated as if they were prostitutes, by society in general. So, they decided to wear white, as a sign of "purity", and to push back.
That aside, it really takes someone like you, to use the KKK as a reference, when you know that quite a few of the Congresswomen/Senators, who wore white, are blacks, and descendants of those who suffered horribly, at the hands of the KKK, and those who supported the KKK.
Or perhaps, as a Canadian, you have no clue what went on in the US, until very recently.