Donald Trump’s call for an ideological litmus test to exclude intolerant foreigners who support Islamic law is redundant, runs contrary to our Founding principles, and could have large potential costs.

American immigration law already excludes entry to, deports, and bars naturalization of foreigners who engage in any activity that supports the overthrow or the control of the U.S. government by force, violence, or other unlawful means. Trump’s ideological test wouldn’t do any more than this already accomplishes, but it could do us serious damage if adopted.

Proponents of ideological screening favorably cite Alexander Hamilton on the topic; “To admit foreigners indiscriminately to the rights of citizens, the moment they put foot in our country, as recommended in the Message, would be nothing less, than to admit the Grecian Horse into the Citadel of our Liberty and Sovereignty.” However, that quote does not support ideological screenings of foreigners.

Hamilton’s essay argues that naturalization, and hence voting, shouldn’t be extended — it’s not about barring the entry of foreigners. Hamilton’s essay seeks to preserve “temperate love of liberty, so essential to real republicanism” in response to President Jefferson’s “proposal to abolish all restriction on naturalization.” Hamilton was arguing in the confines of current law. Congress’ Naturalization Act of 1790 only restricted when and which immigrants could become naturalized (become citizens) but it did not restrict their movement here.

Catholicism was the ideological threat that so concerned Hamilton, the other Federalists, and many of the Founders. Rather than cite Hamilton, proponents of ideological litmus tests should focus on John Jay who wanted to build a “wall of brass” around the country to keep out Catholics. But even here, Jay’s actions aren’t as supportive as modern litmus-test enthusiasts might claim.

Jay’s rhetoric was inflammatory but he, like Hamilton, focused on keeping Catholics from participation in government. Jay introduced amendments to the New York state constitution to deny Catholics property and civil rights unless they denounced the papacy. They failed, but he was able to insert a stipulation that “all Persons holding Offices under the Government should … renounced all allegiance and Subjection to foreign Kings, Princes, and States in all matters ecclesiastical as well a civil [emphasis added].” Jay pushed to exclude Catholics from the government, not the country.

We should rejoice that the Founders eschewed ideological litmus tests for immigrants — preferring to keep them out of the government or the ballot box rather than the country all together. While far too restrictive, their proposed policies were less damaging than total exclusion from the country as a whole. Unfortunately, the Progressive Era and later periods went all in for ideological screening.

The folly of restrictive litmus tests is summed up in the example of Qian Xuesen, a young rocket scientist who emigrated from China in 1935. Theodore von Karman, legendary aerospace engineer, mathematician, and physicist, pronounced Qian an “undisputed genius.” Qian helped the U.S. war effort by researching jet propulsion, rockets, and then joined the Manhattan Institute. In 1949, he was named the first Director of Caltech’s Jet Propulsion Lab. Then immigration law and U.S. paranoia at the beginning of the Cold War unraveled him.