Jefferson was very human and in some ways our quintessential "founder." He had towering strengths: intellect, skill with words, sense of what could be. He had towering flaws: spendthrift (even by planter standards), political knife artist, hypocrite (opposed slavery yet did not manumit much during his life). In short, he embodied the best and the worst of us -- a very human man and a compelling figure to study.
I concur with the suggestion of McCullough's Adams. I'd add (though this is from a later period) Kearns on Lincoln.
Bookmarks