Former first lady Barbara Bush

On June 6, 1964, George Bush, candidate for the Republican nomination for the U.S. Senate, gets returns by phone at his headquarters in Houston, along with his wife, Barbara.

Former President George H.W. Bush and wife Barbara congratulate their son George W. Bush in Austin, Texas, after the younger Bush’s inaugural address for a second term as Texas’ governor in January 1999.

First lady Barbara Bush reacts after President George H.W. Bush accidentally stepped on her toe while boarding Air Force One at Andrews Air Force Base, Md., for a flight to New Jersey on Sept. 22, 1989.

U.S. Vice President George H.W. Bush and wife Barbara Bush lead the Columbus Day Parade in Chicago on Oct. 13, 1986. With them are Mayor Harold Washington, left, and Illinois Gov. James Thompson.

Former President George H.W. Bush and former first lady Barbara Bush point from their seats at the Republican National Convention in St. Paul, Minn., in 2008. The convention nominated Arizona Sen. John McCain for president and Alaska Gov. Sarah Palin for vice president.

Former first lady Barbara Bush leaves the East Room of the White House in July 2013 after an event hosted by President Barack Obama to honor the 5,000th Daily Point of Light Award winner. The award had been established by President George H.W. Bush in 1989 to honor volunteerism.

First lady Barbara Bush and her granddaughter Marshall Lloyd Bush visit with family dog Millie and her six puppies in the White House in 1989. Millie, a springer spaniel, was the namesake of a book that offered a dog’s-eye view of the presidency.

Barbara Bush and former President George H.W. Bush watch the afternoon session of the second day of the Ryder Cup at Medinah Country Club in Medinah on Sept. 29, 2012.

First lady Barbara Bush poses with her dog Millie, a springer spaniel, in 1990.

First lady Barbara Bush walks in the Columbus Day Parade in Chicago on Oct. 9, 1989, flanked by Lt. Gov. George Ryan, from left, U.S. Rep. Marty Russo, Rep. Frank Annunzio, Mayor Richard M. Daley and state Treasurer Jerry Cosentino.

President George H.W. Bush and first lady Barbara Bush walk with Millie, the family dog, across the South Lawn as they return to the White House on Aug. 24, 1992.

Former first ladies Barbara Bush, left, and Laura Bush take part in the Enduring Legacies of America’s First Ladies conference in Austin, Texas, on Nov. 15, 2012.

Barbara Bush, center, jokes with her son Jeb, a Republican presidential candidate and former Florida governor, as she introduces him at a town hall meeting in Derry, N.H., in February 2016.

First lady Barbara Bush greets first lady-to-be Hillary Clinton upon her arrival at the White House in November 1992. Arkansas Gov. Bill Clinton defeated President George H.W. Bush in his bid for re-election.

Entertainer Bob Hope, right, applauds as President George H.W. Bush kisses his wife, Barbara, during a pre-election rally at the Astro Arena in Houston on Nov. 2, 1992.