This excerpt from Leo Rosten’s People I have loved, known, or admired, ©1970, recalls an episode he uncovered while researching George Washington’s life:
But I cannot forget the episode involving Washington as he was being escorted down the street of a town in New York by an official. An old Negro saw the General and stopped and bared his head and bowed. Washington at once doffed his hat, and returned the bow. The flabbergasted politician expressed surprise that the General had bared his head to a slave. Washington replied, “But I cannot be less civil than a poor Negro.”
Presidents in my lifetime who I do not believe would bare their head and bow include Ronald Reagan, George H. Bush, and certainly not Donald Trump.
Presidents in my lifetime who I believe would return the courtesy would be Lyndon Johnson, Richard Nixon, Gerald Ford, certainly Jimmy Carter, George W. Bush, and Barack Obama (once the press had been alerted).