You are right, they know there is nothing they can do.
What they hope for is to create a spectacle, and entice the candidate to say something that can be twisted and lied about to sway the weaker minds in the Republican Party who get their information from the Left-controlled media.
Just read on twitter how the commie Dems in the Senate were planning this over the weekend, getting their paid protestors ready to go for today..I hope sane people see what the commie party is ALL about..the Commies are TERRIFIED that once Kavanaugh gets in, their commie utopia is FINISHED, they know they will NEVER get the Supreme Court again