While riding in a motorcade in Dallas, Texas, President John F. Kennedy is shot and killed. Vice President Lyndon Johnson takes the oath as President, but the Vice Presidency then remains vacant for more than a year until the next election. Johnson had suffered a heart attack several years earlier, and the Speaker of the House and president pro tempore of the Senate, next in line of succession, are both elderly men. Congress acts to rectify this situation by sending to the states the Twenty-fifth Amendment.