It was pretty obvious in retrospect that the Senate was the target. Trump campaigned primarily for Senators.
Also, I've wondered since the beginning why it appeared that a disproportionate share of House Repubs were resigning / not running. I wondered why Q team appeared to be going after Repubs more than Dems . . . I wondered if maybe it was safer and easier to get rid of corrupt Repubs at that time. If getting rid of corrupt congress-critters was the goal, they had to start somewhere.