John Adams the 2nd president of the USA was most definitely not a Christian. He was nothing more than a universalist who rejected the Triune God. Below are a few quotes ascribing him to this belief. You can find a great deal of these quotes in a this book.
In correspondence with Jefferson, we see why Adams was definitely not a Christian,
"θέμίς was the Goddess of honesty, Justice, Decency, and right; the Wife of Jove, another name for Juno. She presided over all oracles, deliberations and Counsells. She commanded all Mortals to pray to Jupiter, for all lawful Benefits and Blessings.
Now, is not this, (so far forth) the Essence of Christian devotion? Is not this Christian Piety? Is it not an Acknonowledgement [sic] of the existence of a Supream Being? of his universal Providence? of a righteous Administration of the Government of the Universe? And what can Jews, Christians, or Mahometans do more?"
Next up will be Thomas Jefferson....