When I was in third grade, we were learning about First Ladies and the history of the president's wife. At one point the teacher called upon a kid who was obviously not paying attention and asked "Why are First Ladies important?"
The kid, with all the confidence of a 9 year old who didn't want to look like they weren't paying attention, responded "Because they were here first."
In 1776, Abigail Adams, wife of future president John Adams, told the First Continental Congress to "...remember the ladies, and be more generous and favorable to them than your ancestors. Do not put such unlimited power into the hands of the Husbands. Remember all Men would be tyrants if they could. If particular care and attention is not paid to the Ladies we are determined to foment a Rebellion, and will not hold ourselves bound by any Laws in which we have no voice, or Representation."
In 1814, as Washington D.C. burned, Dolley Madison stayed in the White House until the very last minute to ensure the nation's treasures that resided there, including the official portrait of George Washington, would not be burned by the British.
In 1850, Abigail Fillmore, who was both wife and teacher to Millard Fillmore, created the White House library, a concession Congress had fought against fearing the power of a personal collection of knowledge for the president, and personally filled in its collection.
In 1919, Woodrow Wilson was heavily debilitated by a stroke. Edith Wilson took over his duties, protecting him from the public, passing on legislation and potentially dealing with it herself. She even went so far as to stage a photo-op to demonstrate the president's continuing capability while she basically Weekend at Bernie's-ed the dude.
In 1933, Eleanor Roosevelt became First Lady and ushered in a new era of political First Ladies. She fought for civil rights, sat on the board of the NAACP, helped created the UN, and set a nearly unmatched standard for powerful women in America.
In 1950, the romance between the young actress Nancy Davis and the actor Ronald Reagan began to shape his political views and ambitions. Her influence pushed him into a political life that lead to his being Governor of California and President of the United States.
In 1963, still covered in the fresh stains of the the day's tragic events, Jacqueline Kennedy stood aboard Air Force One to oversee the official transfer of power from her late husband to Lyndon Johnson.
In 2017, the nation's first female president may well be Hillary Clinton, a First Lady built from Eleanor Roosevelt's mold and the only First Lady to ever ever held an elected office.
I've seen a lot of people grumbling that the potential first female president is married to another president. Why is the first major female candidate for president also a First Lady?
Because they were there first.