Grace Coolidge represents a 20th century first lady whose stunning beauty and charm countered the president's dour and taciturn image, so much so that he began to fear that she was upstaging him.
Other presidential spouses have substituted for ill or handicapped husbands. Edith Wilson is said to have run the White House in the wake of Woodrow's debilitating stroke in 1919. Prior to the 25th Amendment's adoption in 1965, no official mechanism existed for addressing an incapacitated chief executive. From the time of Franklin Roosevelt's paralysis from a bout of polio in 1921, his wife Eleanor served as his "legs," traveling around the nation and world on fact-finding missions for FDR.
Sometimes first ladies must stand in for a politically handicapped husband. In the wake of his signing the Civil Rights Act, Lyndon Johnson faced staunch opposition in the South, so he sent Lady Bird on a whistle-stop tour of the region during his 1964 presidential campaign. JFK had initially proposed the landmark legislation, and his approval ratings were dropping in the fall of 1963, which is why he was so pleased that his wife, who rarely accompanied him on domestic political trips during his presidency, agreed to visit Texas with him that November. Two of the most recent FLOTUSes, Laura Bush and Michelle Obama, both outpaced their husband's popularity ratings and served as powerful surrogates on the campaign trail.
In the case of Hillary Clinton, the first lady had no gap to fill but, rather, assumed a full policy partnership, at least at the beginning of the 42nd president's administration. Bill Clinton had declared during the 1992 campaign that voters would acquire "two for the price of one" if he and Hillary moved into the White House. President Clinton reasoned that she had accepted policy leadership on education and child welfare issues during his Arkansas governorship, so why shouldn't she play an equal role in the presidency?
The American people have a way of answering that question by drawing a distinct line between the levels of first lady activism they are willing to accept and those they aren't. After her leadership of health care reform came under criticism and the administration's initiative failed to pass, Mrs. Clinton returned to a more traditional posture in her duties. She supported women's rights around the world and reactivated her advocacy of children's welfare, but she left testimony on Capitol Hill to administration officials.
Modern first ladies, starting with Eleanor Roosevelt, who is sui generis in the mark she left on the office during her unprecedented dozen years in the White House, can be placed on an activism spectrum. She and Hillary Clinton own the spot of most activity in promoting a variety of policy positions. In fact, Mrs. Roosevelt occasionally frustrated her husband by taking stands that were more liberal than his own, on race and immigration, for example.
At the opposite end of the spectrum are Bess Truman, Mamie Eisenhower and Pat Nixon, who were content to work in their husbands' shadow. Indeed, Mrs. Truman avoided the spotlight and preferred to spend time away from Washington in her hometown of Independence, Mo.
Source : https://www.dallasnews.com/opinion/commentary/2018/12/30/how-a-few-first-ladies-used-their-narrow-role-for-big-influence