The argument goes that the United States was founded as a Christian Nation, by Christians for Christians and anybody who disagrees can just shut the fuck up. However, a lot of the founding father's were deists. They honestly had to be. They were going against the king, God's chosen ruler, and that's not something good Christians do. It was about half a dozen presidents before we hit a real Christian. However, if the logic still holds here, might I offer a stronger argument?
The United States was founded as a White Nation. All of the founding fathers have been white. All of the presidents have been white. Rather than demanding religious freedom for all religions in the constitution, which goes against the Christian Nation idea, it was rather clearly spelled out that the freedoms only extended to whites.
Why is it that this nation is a Christian nation, but not also an English-Speaking, White, Male nation? Certainly those who demand white supremacy quite often advocate Christian supremacy as well. Everything old is new again.
We are also seeing the exact same arguments recrafted from the ashes of the interracial marriage debates rehashed in the gay marriage debates. Oh, if God wanted the races to marry they would have put them on the same continents, and God made Adam and Eve not Adam and Steve.
It should also be noted, that since God has no logical foundations, one can just trot the character out as a walking fallacy. With a fallacy you can prove everything (which is why they are worthless). With faith, all things are possible. With God, all things are possible. So having your personal fallacy ready and willing, with built in taboo of criticism no less, one can provide an argument for indefensible bigotry.
If there are only religious arguments for something, then there are no good arguments for it.