The reasons stated by some of the historians for their choice of the presidency that they believe Bush's to be the worst since are worth repeating. The following are representative examples for each of the presidents named most frequently:
REAGAN: "I think the presidency of George W. Bush has been generally a failure and I consider his presidency so far to have been the most disastrous since that of Ronald Reagan--because of the unconscionable military aggression and spending (especially the Iraq War), the damage done to the welfare of the poor while the corporate rich get richer, and the backwards religious fundamentalism permeating this administration. I strongly disliked and distrusted Reagan and think that George W. is even worse."
NIXON: "Actually, I think [Bush's] presidency may exceed the disaster that was Nixon. He has systematically lied to the American public about almost every policy that his administration promotes." Bush uses "doublespeak" to "dress up policies that condone or aid attacks by polluters and exploiters of the environment . . . with names like the ?'Forest Restoration Act' (which encourages the cutting down of forests)."
HOOVER: "I would say GW is our worst president since Herbert Hoover. He is moving to bankrupt the federal government on the eve of the retirement of the baby boom generation, and he has brought America's reputation in the world to its lowest point in the entire history of the United States."
COOLIDGE: "I think his presidency has been an unmitigated disaster for the environment, for international relations, for health care, and for working Americans. He's on a par with Coolidge!"
HARDING: "Oil, money and politics again combine in ways not flattering to the integrity of the office. Both men also have a tendency to mangle the English language yet get their points across to ordinary Americans. [Yet] the comparison does Harding something of a disservice."
McKINLEY: "Bush is perhaps the first president [since McKinley] to be entirely in the ?'hip pocket' of big business, engage in major external conquest for reasons other than national security, AND be the puppet of his political handler. McKinley had Mark Hanna; Bush has Karl Rove. No wonder McKinley is Rove's favorite historical president (precedent?)."
GRANT: "He ranks with U.S. Grant as the worst. His oil interests and Cheney's corporate Haliburton contracts smack of the same corruption found under Grant."
"While Grant did serve in the army (more than once), Bush went AWOL from the National Guard. That means that Grant is automatically more honest than Bush, since Grant did not send people into places that he himself consciously avoided. . . . Grant did not attempt to invade another country without a declaration of war; Bush thinks that his powers in this respect are unlimited."
ANDREW JOHNSON: "I consider his presidency so far to have been the most disastrous since that of Andrew Johnson. It has been a sellout of fundamental democratic (and Republican) principles. There are many examples, but the most recent would be his successful efforts to insert provisions in spending bills which directly controvert measures voted down by both houses of Congress."
BUCHANAN: "Buchanan can be said to have made the Civil War inevitable or to have made the war last longer by his pusillanimity or, possibly, treason." "Buchanan allowed a war to evolve, but that war addressed a real set of national issues. Mr. Bush started a war . . . for what reason?"
I particularly found the Harding entry rather amusing. But all of these historians seem to have a good grasp on the situation.
source
is here