My analysis takes circumstances into account. Interesting times give presidents the opportunity to achieve either greatness or ignominy.
Washington, Lincoln, FDR, and Truman all inherited very challenging circumstances, but nevertheless earned greatness by rising to the occasion.
Buchanan inherited a terrible mess he had helped create as a longtime political insider. He made it worse by sticking to a strategy of craven appeasement that ultimately constituted treason.
Nothing in Trump’s long life or short presidency suggests he could have outperformed any of his other predecessors, including Buchanan. This country has never before elected anyone so obviously unfit, comprehensively incompetent, astonishingly ignorant, audaciously dishonest, brazenly corrupt, openly contemptuous of democracy, and shamelessly servile to foreign despots.
Fortunately, happier circumstances and successful resistance will probably prevent Trump from matching the damage Buchanan did to this country.