The Tafts (William and Robert), the Adamses (John, John Quincy, etc.), and even the founder of the John Birch Society, Robert Henry Winborne Welch Jr., were Unitarians.
... and unitarians deny the trinity. In most cases, this means they deny the divinity of Christ. (In some cases, unitarians believe Christ was divine, but deny that there is any sense in which Christ was distinct from the Father, but this is rare.) I do not claim to know much of the Tafts beliefs, in particular, however.
... actually, I just looked up and found that when John Quincy Adams’ congregational church (which had been John Adams) veered into unitarianism, Adams attended a debate between trinitarian Samuel Adams and unitarian William Channing, and found Sam’s position so superior, he denounced that church. That also tells me that when John “Sr.” attended the church, it could not have been unitarian.
Later, he became far more ambiguous, stating, “But neither this, nor any other argument that I ever heard, can satisfy my judgment that the doctrine of the Divinity of Christ is not countenanced by the New Testament. As little can I say that it is clearly revealed. It is often obscurely intimated; sometimes directly, and sometimes indirectly, asserted; but left on the whole, in a debatable state, never to be either demonstrated or refuted till another revelation shall clear it up.”
He, however, continued to attend Presbyterian and Episcopal churches more frequently, and bitterly opposed as diabolical the teachings of emerging unitarian leaders such as Joseph Priestly and Ralph Waldo Emerson. (He also thought Priestly was WAAAY to old-looking to play a high school kid :^D.)
Actually, having read the Jefferson Bible, I might, however, suppose Jefferson to be unitarian. He seemed to reject any portion of the bible which attributed divinity in any form, including most miraculous works, to Jesus.