Eventually, the police arrived. I was fortunate that the responding officers were well educated on First Amendment laws and did not try to stop me from taking pictures.
The incident raised a number of ethical questions. I’ve been castigated by a number of anonymous internet commenters who have said that I should have somehow physically intervened between the two. Their criticism counters what actual law enforcement officers have told me — that physically intervening would have likely only made the situation worse, endangering me, and further endangering Maggie.