It may be a joke.
I think it was the leftist group "NOW', but I am not sure.
Anyway, when Gorsuch was approved by the senate vote, some leftist group let out a press release saying some thing like "The confirmation of Justice _______ to the Supreme court was a set back for people .........etc,etc,etc"
The press release was on file with this group, they just had to fill in the blank with the(any) conservative justice's name and send it off.
The fools sent it off before putting Gorsuch's name in the blank spot.
So, maybe there was a fill-in-the-blank assault accusation letter, but I think this is most likely a joke, based on the Gorsuch press release.