President Trump may have been charmed by Zohran Mamdani, but the mayor-elect’s response to the anti-Israel mob that turned up at Park East Synagogue this week was shocking and telling in equal measure. To the braying of “Death to the IDF” Mr. Mamdani said, through his press secretary, Dora Pekec, that he “has discouraged the language used” at the protest and “will continue to do so.” What a milquetoast response to a hateful protest. 

What came next was even worse. Ms. Pekec added that her boss, who was about to meet the president, “believes every New Yorker should be free to enter a house of worship without intimidation, and that these sacred spaces should not be used to promote activities in violation of international law.” The reference is to Nefesh B’Nefesh, which was holding an event at Park East. The group helps Americans and Canadians who want to move to Israel. 

Put aside the impropriety of an elected official lecturing a house of worship about what it should do in its “sacred space.” More concerning is Mr. Mamdani’s obsession with “international law,” particularly given that he will soon swear an oath to “support the Constitution of the United States, the Constitution of the State of New York, and the New York City Charter.” Treaties of which America is a party are part of the “Supreme law of the land.”

So much for international law. Mr. Mamdani’s view appears to stretch far beyond our treaties. He told the Times in September that if Prime Minister Netanyahu visits New York City he intends to order the NYPD to arrest him out of his “desire to ensure that this be a city that stands up for international law.” Mr. Mamdani’s allusion appears to be to the arrest warrant issued for the premier of the Jewish state by the International Criminal Court.

Mr. Mamdani said just this week that “Being a city of international law means looking to uphold international law. That means upholding the warrants from the International Criminal Court, whether they’re for Benjamin Netanyahu or Vladimir Putin.” America, though, is not a signatory — thank goodness — to the Rome Statute. That’s the treaty that created the ICC. So it’s hard to see where “international law” reaches any American.

For Mr. Mamdani “international law” appears less a high-minded appeal to global norms than a means of expressing antipathy to Israel. Mr. Mamdani has not, to our knowledge, expressed an opinion about what kind of programming should be held in any houses of worship besides a synagogue. He did, however, appear at a mosque with an unindicted co-conspirator in the 1993 World Trade Center bombing, Siraj Wahhaj, who has celebrated jihad.

The ways in which “international law” has been corrupted into a cudgel against the Jewish state go far beyond Mr. Mamdani, but his invocations of its authority are a threat to Jews and an affront to American sovereignty. The group that organized the protest at Park East, Palestinian Assembly for Liberation, calls El Al “Genocide Settler Airlines” and considers every person who moves to Israel to be a “settler,” no matter their final destination.

International law is often evoked by the world’s scoundrels as a fig leaf for acts of aggression. This week a spokeswoman for Communist China, Mao Ning, declared that “the erroneous remarks of Japanese Prime Minister Sanae Takaichi on Taiwan … trample on international law and basic norms.” Ms. Takaichi’s sin, so to speak, was to suggest that an attack from Beijing on Taiwan could trigger a reaction from Tokyo.

Champions of international law like Mr. Mamdani have been notably silent in the wake of the Security Council’s endorsement of President Trump’s 20-point plan for Gaza. Security council resolutions are, under the United Nations charter, binding international law for all member states, of which America is one — for now. Mr. Mamdani’s interest in the world’s law appears piqued only when it can be used against the Jews.