I am currently reading “Jefferson The Virginian” by Dumas Malone. It’s the first of six books about Jefferson which eventually earned him the Pulitzer Prize. I unfortunately don’t have the book with me to quote from, but Jefferson came out against slavery (in writing) before 1776.
John / Billybob
American Sphinx by Joseph Ellis is good too, though some discount it on account of the author's bogus claims of serving in Vietnam. His book on Washinton, 'His Excellency', is also worth reading.