Readers of Just Security may find of interest the letter that my colleagues and I at Georgetown Law’s Institute for Constitutional Advocacy and Protection sent today to President Trump warning that his recent anti-Muslim tweets are at odds with the First Amendment. Our co-signatories include a diverse range of faith-based organizations, and we’ve come together to emphasize that the President overstepped key constitutional guarantees when he recently retweeted three unverified videos with anti-Muslim captions. The letter notes that President Trump and his administration have indicated that messages emanating from his @realDonaldTrump Twitter account constitute official statements of the President. The letter goes on to explain that, although the government enjoys considerable latitude in deciding what messages to express, the President’s anti-Muslim tweets sit in tension with critical protections articulated by the Supreme Court in interpreting the First Amendment’s Establishment Clause. In particular, the letter cites several major cases in which the Court has said that the government may not display “animus toward religion” or “hostility” toward a particular faith, and furthermore may not “prefer one religion to another.” Ultimately, we hope that this letter helps the President and those advising him to appreciate the constitutional boundaries that courts have articulated to uphold the First Amendment’s guarantees with respect to religion.