Joseph Priestley's Biblical Defense of Unitarianism:

Theological unitarians disproportionately influenced the American Founding. Joseph Priestley (co-discoverer of oxygen) was the theological mentor to Jefferson, J. Adams and Franklin. Madison appealed to the Arian heretic Samuel Clarke (not John Witherspoon) when asked to put his theological cards on the table. Richard Price was especially influential. And of course John Locke and Isaac Newton, figures revered by America's Founders were likely secret unitarians. John Adams and Thomas Jefferson never really gave serious philosophical or biblical rebuttals to the doctrine of the Trinity. They tended to bitterly mock it and related orthodox doctrines, seeing it as a self evident falsehood.

Their theological mentor Joseph Priestley however, did get into the philosophical trenches and argue against the Trinity (and Jefferson & J. Adams tended to simply appeal to his authority). Though Priestley, like America's key Founders, didn't believe the Bible infallible -- indeed he held the "plenary inspiration of the Bible" to be a classic "corruption of Christianity" -- he did make a strong biblical case AGAINST Trinitarianism. You may read it here and here.