WHO is the odd man out in this group?: George H. W. Bush. Bill Clinton. George W. Bush. Barack Obama.
Easy. It's George H.W. Bush, the only one of those (so far) to be denied a second term - but the only president in the group who was not a viscerally polarizing figure.
Though no president since Calvin Coolidge, with the possible exception of Dwight Eisenhower, has escaped strong partisan controversy, the level and intensity of opposition to the last three presidents marks either a great departure from the American norm - or the establishment of a sad new norm in our politics.
Not since the first President Bush, who didn't have an easy time with the electorate but found perhaps his strongest adversaries among rebel members of his own Republican Party, has a president sat in the White House without being attacked by a virulent strain of hostile opposition.
Indeed, the last three presidents have been described as unfit for office for being, variously, philanderers, war criminals, and socialists.
In part the level of opposition matches the level of political skills of the last three presidents, the first a fluent master of the stump speech and of the tiniest detail of policy; the second a canny survivor underestimated by foes who thought him unintelligent and ungifted, and the third an unflappable, cerebral personality whose greatest asset and vulnerability may lie in his profile as a departure itself from the presidential norm.
Presidents have never had a blithe passage through the White House. Woodrow Wilson once described Chester Arthur as "a nonentity with side whiskers." Abraham Lincoln characterized James K. Polk as "a bewildered, confounded and miserably perplexed man." Harry Truman once described Richard Nixon as "a shifty, goddamn liar, and people know it." Andrew Jackson once referred to William Henry Harrison as "the present imbecile chief."
But there seems to be a special shrillness, a particular meanness, to the attacks focused on recent presidents, a bitter harvest that Mr. Obama now seems to be reaping.
Part of it, of course, is retribution, which, perhaps even more than money, is the mother's milk of politics. One president gets attacked viciously because the last one did. Turnabout is fair play - it's more than a proverb, it's a political playbook.
And yet there is a different quality of opposition to Messrs. Clinton, Bush, and Obama than there was to some of the more recent deeply unpopular presidents, such as Lyndon Johnson, Nixon, and Jimmy Carter.
Perhaps a hint for this new level of hostility can be discerned from the opposition to those three earlier presidents, each of whom sowed strong opposition from within his own party.
Johnson was challenged for renomination by two Democratic senators, Eugene McCarthy and Robert Kennedy, before standing down from the contest in 1968. Nixon faced small party rebellions from both the Republican left (Pete McCloskey) and right (John Ashbrook) when he sought re-election in 1972 before losing the support of GOP stalwarts in the impeachment crisis of the summer of 1974. And Mr. Carter faced a strong Democratic insurrection and then a renomination challenge from Sen. Edward Kennedy when he ran for re-election in 1980.
Though besieged by critics, none of the three most recent presidents, once elected, faced strong intra-party rivals or had to deal with substantial party fissures.
Mr. Clinton never was in danger of conviction after being impeached in 1998 because Democrats in the Senate were not inclined to strip him of office. George W. Bush's strongest Republican opponent was Sen. John McCain, who throughout most of the Bush years shaped a workable truce with the president. No Democratic rival to Mr. Obama is in sight, nor are there vocal Obama skeptics within the Democratic Party.
Indeed, the last three presidents are mostly the targets of angry and vocal opponents from outside their parties. Mr. Bush, whose popularity sank in his last years, may have become a Republican punch line but he never became a Republican punching bag.
Truman once said that being president is like riding a tiger: "A man has to keep riding or be swallowed." Today's ride is harsher than ever, perhaps because talk radio and cable TV shows thrive on provocation and rage, perhaps because the depersonalized nature of the Internet fosters acrimony and enmity, perhaps because the culture of the age is suffused with fury, outrage, and indignation.
Truman served in a Senate with conservative Democrats and liberal Republicans, and as president the ideological diversity within the parties gave him more maneuverability, and more opportunity for bipartisanship, than Mr. Obama possesses today. The parties in the Obama era not only are more disciplined and ideologically coherent, they also are more partisan.
"We have homogenous parties now, and there are no cross pressures within them," says George C. Edwards III, who holds a chair in presidential studies at the George Bush School of Government and Public Service at Texas A & M University.
"It's built-in that you're not going to like the president of the other party. This is aggravated by the echo-chamber produced by the new network of news, which tends to be more ideological and has new ways of reaching and inflaming the public. Today you can't just disagree. You have to say the president of the opposition party is trying to tear down America."
George Washington, who knew his early actions would be regarded as presidential precedents rather than personal prejudices, conceived of the presidency as a great office of unity - so much so that, in one of the great presidential metaphors of all time, he and his wife actually arranged 16 marital unions, Dolley and James Madison among them.
"As president," Gordon Wood writes in his magisterial new volume, Empire of Liberty, Washington "spent much of his time devising schemes for creating a stronger sense of nationhood."
The irony now is that, in maturing, the American presidency is so often a wedge of disunity. Americans need to fix that, to fix their country.
David Shribman is executive editor of the Pittsburgh Post-Gazette.
Contact him at: firstname.lastname@example.org