In the United States, clergy never had formal political power. Religious movements did play major roles in the abolition of slavery and Prohibition of alcohol.

The United States had campaign-finance laws to limit the political influence money can buy. The McCain–Feingold Act restricted “dark money”. The Supreme Court struck it down in Citizens United v. FEC.

I think he’s referring to the separation of church and state that was codified at the founding of the US based on experience of how things went in Europe prior to that