First, the presidency of Richard Nixon, in whose White House I served from its first day to its last, covered in my new book, "Nixon's White House Wars: The Battles That Made and Broke a President and Divided America Forever."

The second has been the astonishing campaign of Donald Trump and his first 100-plus days as president.

In many ways, the two men could not have been more different.

Trump is a showman, a performer, a real estate deal-maker, born to wealth, who revels in the material blessings his success has brought. Nixon, born to poverty, was studious, reserved, steeped in history, consumed with politics and policy, and among the most prepared men ever to assume the presidency.