When Did Jefferson Become Anti-Trinitarian

I see Thomas Jefferson's July 25 1788 letter to Derieux as expressing unitarian sentiments, and claiming to have done so his entire adult life. Still, perhaps it isn't a smoking gun of anti-Trinitarianism (as Tom Van Dyke suggests). Yet, I think such smoking guns exist well before David Barton's claim of 1813. For instance, Jefferson's April 21, 1803 (while he was President!) letter to Benjamin Rush where Jefferson discusses his Syllabus. In the letter to Rush, Jefferson states:

To the corruptions of Christianity I am indeed opposed; but not to the genuine precepts of Jesus himself. I am a Christian, in the only sense he wished any one to be; sincerely attached to his doctrines, in preference to all others; ascribing to himself every human excellence; & believing he never claimed any other.

As I read the passage, Jefferson seems clearly to say that Jesus never claimed to be anything other than human. That is anti-Trinitarian. Likewise "Corruptions of Christianity" was termed by Jefferson's mentor, Joseph Priestley who defined those corruptions as Original Sin, Trinity, Incarnation, Atonement, and Plenary Inspiration of the Bible. Immediately after Jefferson sent his Syllabus to Rush, he then sent a copy to Priestley, with a note. Jefferson does tell Priestley there may be "a point or two in which [they] differ." Indeed, Jefferson later explicitly rejected the Virgin birth and Resurrection, both of which Priestley believed. Jefferson says to Priestley his Syllabus "omits" the question of Jesus' divinity. The Syllabus itself claims the issue of Jesus being a member of the Godhead is "foreign" to the view expressed in the Syllabus. The overall context of these communications seems firmly unitarian. Though I see the quotation to Rush that Jesus never claimed anything other than "human excellence" as anti-Trinitarian.