As an official in the Justice Department, I followed in Hamilton’s footsteps, advising that President George W. Bush could take vigorous, perhaps extreme, measures to protect the nation after the Sept. 11 attacks, including invading Afghanistan, opening the Guantánamo detention center and conducting military trials and enhanced interrogation of terrorist leaders. Likewise, I supported President Barack Obama when he drew on this source of constitutional power for drone attacks and foreign electronic surveillance.But even I have grave concerns about Mr. Trump’s uses of presidential power.