A national-security investigation may “not [be] conducted solely upon the basis of activities protected by the first amendment to the Constitution.” That clause, and others similar to it, are found throughout the Patriot Act and other provisions of federal law. They protect Americans from being subjected to surveillance based on nothing except their religious beliefs.
There’s an obvious reason for that — at least, I thought it was obvious until Donald Trump reportedly embraced the idea of forcing Muslims to register in a database. I say “reportedly” because it is not clear to me, after hearing a recording of Trump’s hectic gaggle with reporters, that he intentionally articulated such a proposal. More likely, he thoughtlessly agreed that it should be considered upon being asked some loaded questions — which is better, but not much.
The reason our law forbids investigations based on religion alone is also spelled out in the Patriot Act. As Section 102 explained: “The concept of individual responsibility for wrongdoing is sacrosanct in American society, and applies equally to all religious, racial, and ethnic groups.”