Mentioned this before, but no, it's not. Article 11 of the Treaty of Tripoli comes right out and says it's not founded on Christianity.
You really can't say that that statement is true or false. If your going to use documents, lets look at our declaration of independence.
"We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.”
Now this creator could be taken as God, or as a father or whatever. There is no true answer to wether the U.S. was founded on Christanity or not. You find that out when you buy your first college history book or, like me, look at your parent's.
Also, the Articles of conferderation mention God wether you want to take it that way or not.
"And Whereas it hath pleased the Great Governor of the World to incline the hearts of the legislatures we respectively represent in Congress, to approve of, and to authorize us to ratify the said Articles of Confederation and perpetual Union."
However, despite all this, our founding fathers did not want a religion at the forfront of this great nation.
Here is the treaty you stated as well.
"As the Government of the United States of America is not, in any sense, founded on the Christian religion; as it has in itself no character of enmity against the laws, religion, or tranquillity, of Mussulmen; and, as the said States never entered into any war, or act of hostility against any Mahometan nation, it is declared by the parties, that no pretext arising from religious opinions, shall ever produce an interruption of the harmony existing between the two countries."
The document has found controversy because of originally being in Arabic.
Most people fall back on the fact that Christians are the majority, which bares no fact.
I feel like I have been talking in circles. Sorry if I have. However, there is no truth to the fact whether or not America was founded on Christanity or not.
2. Let's not start playing the truth game. Both sides ultimately win. If you go from one side, yes Christians have to bring the proof that God exists. If you go to the other side which we use in our court systems, then Atheist have to prove that God doesn't exists. This just leads to a stall war.