I can assure you that the Senate is 100% wise to Trump's abuse of the "acting" cabinet member positions, but the GOP Senate majority has decided that they'd rather not be bullied on Twitter. Congressional GOP's skimping of oversight duties will go down in history either as the most tremendous things friends have ever done for one another in the whole entire universe (all of it, folks), or treason.
One of the strangest developments of the previous decade or two is the idea that Congress works for the president. That's basically antithetical to the way separation of powers is supposed to work. Even the president's cheerleaders in Congress are supposed to feign giving him the business now and then just to make sure they can get what they want when they want it. I think the Iraq War broke the system in ways we're still only beginning to appreciate.