Yes, 2000 years of established legal/social foundations and Obama signing something are exactly the same thing.
2,000 years of “tradition” (and there are all kinds of traditions, eg religious pluralism vs burning heretics) don’t determine US law. What’s legally determinative is the text of laws, not some intentions that you self-servingly purport to divine. And you’re wrong that “the Founders” intended the US to be a Christian state. Various Founders had various views. For example, Jefferson and Madison both denied Jesus’ divinity, disparaged Christianity, and detested the intertwining of religion and state.