Trump’s purportedly treating the Constitution like a spittoon. Former Acting Solicitor General Neal Katyal appearing on “The Last Word” with Ali Velshi on Friday hammered the 45th president’s theory that as POTUS he can do anything he wants and remain untouchable. “We have had 46 presidents — no one has claimed absolute immunity from the criminal law,” Katyal said. “And now Donald Trump comes along and does so.” POLL: Should Trump be allowed to run for office? He continued: “He is spitting on our Constitution. He is spitting on our rule of law. And I cannot think of a more disqualifying statem…