The founders knew it, and stated it plainly in the declaration of indepence.
Paul went so far as to say creation itself shows God to be real, and that men who reject Him are without excuse.
On my own, I found it to be self evident as well (at a time that I would have prefered Him not to exist).
There are several proofs of God. The most obvious being the one referenced by Saint Paul. To outline breifly:
Primise 1: There is "stuff".
Premise 2: Stuff changes state, but can not be created or destroyed within natural law (modern man has seen that matter can be converted to energy and back, but both of these things are still "stuff" changing state).
Deduction 1 (from premise 1 and 2): Unless natural law was interupted by a trascendent power (to create stuff), there must have always been stuff.
Premise 3: Not everything that will happen has happened yet.
Deducton 2 (from premise 3): There has not been enough time for everything that has happened to happen.
Deduction 3 (from deduction 2): Stuff has not always existed.
Deduction 4 (from deduction 1 and deduction 3): A trascendent power created stuff.
Note, this is not as formal as philosophers like to make this stuff, but is just an outline. There are some objections that can be raised, but so far I have found them all falacious.
WT id that be set up. Word to you.