He doesn’t need Constitutional authority. The Constitution is moot if the other branches of the federal government and we the people are willing to stand by and allow this brazen lawless corruption of our system!
“Power perceived, is power achieved.”
Yes, we the people must work to return the states to the senate. Our Framers didn't rely on, as per Madison, “parchment barriers.” Their freedom enhancing design relied first and foremost on federalism, the vertical separation of power between the states and the federal government they created. Until the senate is de-democratized, raw power will continue to accumulate in the executive and judicial branches.