While I knew that Abraham Lincoln is credited with establishing Thanksgiving Day as a national holiday, I didn’t know it had previously been the custom of presidents and governors and others to declare “a day of Thanksgiving” on a regularly occasional basis. (That is, they did this regularly, but according to no set calendar.) So in addition to the thanksgiving celebration of the pilgrims we know so well, George Washington twice declared days of national thanksgiving (in 1789 and 1795). John Adams and James Madison did the same on several occasions (though Jefferson never did). While often these days of thanksgiving were declared to...