Gov. Gavin Newsom’s proposed constitutional amendment on gun safety has two great things going for it. The first is that it aims to protect four popular and modest commonsense restrictions: a ban on assault weapons, mandated background checks on gun buyers, a waiting period before buyers can take possession, and a minimum purchasing age of 21. All four requirements are already law in California, where they contribute to a gun death rate that’s about 37% lower than the national average. All four are currently in peril as the U.S. Supreme Court continues to strike down reasonable gun laws. Under Newsom’s...