AMID ALL THE frenetic early maneuvering in the 2008 GOP presidential race, Republicans may be missing the elephant in the room: namely that the head of the herd is bleeding to death on the carpet. ~Ron Brownstein

As Yglesias has already cited:

Democrats lost the White House in 1952 and 1968 after Harry Truman and Lyndon Johnson saw their approval ratings plummet below 50%. Likewise, in the era before polling, the opposition party won the White House when deeply embattled presidents left office after the elections of 1920 (Woodrow Wilson), 1896 (Grover Cleveland), 1860 (James Buchanan) and 1852 (Millard Fillmore). The White House also changed partisan control when weakened presidents stepped down in 1844 and 1884. Only in 1856 and 1876 did this pattern bend, when the parties of troubled presidents Franklin Pierce and Ulysses S. Grant held the White House upon their departure.

Those deeply embattled Presidents also usually had large domestic problems that had helped drive the their administrations into the ground: secession, depression and recession formed the backdrops to the ’60, ’96 and ’20 elections respectively.  The 1876 result is also misleading and gives Republicans more hope than they should have, since Tilden the Democrat would have been President, had it not been for the Reconstruction-ending bargain that gave the election to Hayes.  A future GOP nominee could, of course, promise to end the occupation of Iraq and imitate Hayes in that way, but unfortunately for him Iraq does not (as of yet) have any votes in the Electoral College, so it could not change the outcome in the same way.

The parallels with 1952 are certainly real and a little eerie, as I have discussed before, but where 2008 differs from all of these other albatross elections is that it is an entirely open (i.e., no incumbents on either side) election during wartime after a full two-term Presidency.  1952 was entirely open, but only because Truman knew he had no chance and therefore followed only about 1.75 terms of the Truman Presidency.  Obviously, Johnson bowed out after winning only one election in his own right.  1920 followed a two-term Presidency and was entirely open, but the war had already been concluded.  Presidents who oversee the beginnings of American involvement in major foreign wars are either personally re-elected or, if the war is going poorly, retire from politics prematurely.  If the President is re-elected, the war typically ends during the second term.  You do have the odd exception of FDR, but repetition of this is now unconstitutional.