I think somebody who isn't practicing Christianity, does not openly accept the tenets of the faith, and shows no interest in the Christian religious vision, most definitely is not a Christian. That covers Tricky Dick.
Most agnostics I know may be skeptical about the received scripture, myths, and rituals of world religions, but they seem to still have a vague interest in spirituality and transcendent wisdom, or at least open to the possibility..
That's not the vibe I get from Tricky Dick or Trumpf who seemed to be self interested, cynical, strict materialists.