They are waiting for Jan. 1, 2020. Then the Hag of D.C. (Ginsberg) can retire in Trump's lame duck year and it will be hard for republicans to defend adding a justice when they fought so hard for the opposite. The Dems will then try to extort the republicans with the most communistic judges they can which will play well in the media during the campaign. For now they don't want republicans to know who they will throw at them so they can't dig into their backgrounds.