Presidents, there is something unique about GWB. Buchanan, Grant and Harding in many ways are not comparable to Bush because of their political naivete and their administrations actual believe in limited government. Bush is not political naive. I think Bush truly believes in a limited government when related to internal affairs, but he feels he is not able to accomplish that goal while he attempts to project America's natural role in world affairs. I think there is such an inconsistency between his attempt to act on his beliefs and his stated conservative beliefs that he is unable to see. For that reason and the stakes involved at this time for America will he go down as one of the worst presidents ever. His administration's track record with telling the truth will be viewed as an integral part of their vision of good governance and will result with his administration being viewed as ethically and morally more trouble than the Nixon administration; without the competence - which for Nixon was mainly confined to foreign affairs.
While I don't want to minimize the Spanish-American War or the Phillipine-American war, they came at a time of when American was increasing its influence and becoming a superpower and a result of arrogance when there was little to check that arrogance. The fact that the Iraqi war happened after the Viet Nam war will only add to the understanding of GWB's inability to think critically about the consequences of his vision of America and its role in the world.
edits: changed ethical to ethically and clarified I was talking about Nixon's competence.