They don't even need to read the Treaty of Tripoli (which I'd be willing to bet most think was made up by some liberal.) Point 'em at a copy of the Constitution and the Bill of Rights and ask 'em to find the bits that talk about God. Anywhere.

They're the founding documents, and the only time they mention religion is in context of nonestablishment. Any establishment.

Then point them to a history of the Pledge. Because I'm stunned at how many people think Jefferson wrote it and it's been recited since Betsy Ross gave us a flag to pledge to.