Ranking Bush
Columbia University History professor Eric Foner in today's Washington Post:

At a time of national crisis, Pierce and Buchanan, who served in the eight years preceding the Civil War, and Johnson, who followed it, were simply not up to the job. Stubborn, narrow-minded, unwilling to listen to criticism or to consider alternatives to disastrous mistakes, they surrounded themselves with sycophants and shaped their policies to appeal to retrogressive political forces (in that era, pro-slavery and racist ideologues). Even after being repudiated in the midterm elections of 1854, 1858 and 1866, respectively, they ignored major currents of public opinion and clung to flawed policies. Bush's presidency certainly brings theirs to mind.
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Historians are loath to predict the future. It is impossible to say with certainty how Bush will be ranked in, say, 2050. But somehow, in his first six years in office he has managed to combine the lapses of leadership, misguided policies and abuse of power of his failed predecessors. I think there is no alternative but to rank him as the worst president in U.S. history.