Trump has been horrible. His crimes have been many, large and small. But history will record this letter from White House Counsel Pat Cipollone formally announcing that the White House rejects congressional authority outright, as the moment when Trump declared war on the constitution.
“President Trump and his Administration reject your baseless, unconstitutional efforts to overturn the democratic process. Your unprecedented actions have left the President with no choice. In order to fulfill his duties to the American people, the Constitution, the Executive Branch, and all future occupants of the Office of the Presidency, President Trump and his Administration cannot participate in your partisan and unconstitutional inquiry under these circumstances,” Cipollone wrote.
Under our system if tripartite government with its three co-equal branches and system of checks and balances, the President is breaking the law by blocking an impeachment inquiry. If this stands we have passed from being a Republic into some new (for us anyway) territory of government by unchallengeable executive.