“I can tell you behind the scenes there is a lot of alarm,” Flake said. “There is concern that the president is laying the groundwork to move on Bob Mueller or [Deputy Attorney General Rod] Rosenstein, and if that were to happen, obviously, that would cause a constitutional crisis.”

He added, “There is concern behind the scenes. I’ve been concerned that we haven’t spoken up loudly enough and told the president, ‘You simply can’t go there.’ And he’s obviously probing the edges as much as he can, to see how far Congress will go, and we’ve got to push back harder than we have.”