The Presidency tends to cause the decline of popularity of those who hold that office, because they have to make controversial and difficult decisions which undermine their image after four or eight years in office.
In the past century, in the time of modern media exposure, which makes the Presidency a national concern on a daily basis, most Presidents, upon leaving office, have seen their public opinion rating collapse, and usually, only after they die, does their image, and respect for the difficult decisions they made, revive their popularity among both scholarly experts and the general public.
This discussion, of course, must eliminate those Presidents who did not survive the office, including Warren G. Harding, Franklin D. Roosevelt, and John F. Kennedy. However, FDR and JFK would remain highly popular in death on a regular basis since their deaths, while Harding’s brief popularity after his tragic death collapsed upon learning of the sex and other scandals during his Presidency, and he has not recovered in ratings by any group.
The only Presidents who remained generally popular after leaving office were Theodore Roosevelt, Dwight D. Eisenhower, Ronald Reagan and Bill Clinton.
William Howard Taft, Herbert Hoover, Gerald Ford, Jimmy Carter, and George H. W. Bush left office after defeat, and none of them were well regarded after their time in office. Carter and Bush had the bad luck of being followed by popular Presidents Reagan and Clinton, and Bush has had the bad luck of having both his predecessor and successor well regarded, making his time in office look quite unimpressive by comparison.
Woodrow Wilson, Calvin Coolidge and Lyndon B. Johnson left office, with each under a cloud of disrepute, with Wilson seeing the defeat of the Versailles Treaty ratification and membership in the League of Nations; Coolidge seeing the coming of the Great Depression crash on Wall Street within months of his retirement; and Johnson having to bear the burden of the Vietnam War: and all three died within four years of retirement, highly unpopular.
Taft regained respect for his service as Chief Justice of the Supreme Court; Richard Nixon gained respect for his foreign policy expertise in his long 20 years of retirement, but did not gain popularity for the rest of his lifetime; Harry Truman also had 20 years of retirement, but only gained popularity and respect after his death; Gerald Ford and Jimmy Carter started to be regarded better as the years went by, with Carter about to surpass Herbert Hoover in longevity after the Presidency, but still condemned by many experts and the general public; and George W. Bush remains unpopular and seems resigned to the fact that he may not gain popularity or respect until he has passed from the scene.
Eisenhower and Reagan retained their public popularity in their post Presidency despite scholarly criticism of their time in office, and both are now regarded more highly, even by scholars, than they were when they were retired and alive.
TR and Clinton share a special bond, as both were young when leaving office; both were highly verbal and opinionated and constantly made news; both had charisma and were loved by the general public in their post retirement years; and TR actually ran for President on a third party line, while Bill Clinton would love to run again, as many Americans wish he could be President again, but of course, the 22nd Amendment prevents that, so instead, the push for his wife, Hillary Clinton, to try for the Presidency again in 2016 is growing!