Actually, the case law I've seen has stated cops have no duty to protect individuals, just society as a whole. For instance, the city of San Jose in Kalifornia is currently being sued by the people injured at a Trump Rally. The city tried to claim they had no duty to protect those injured by the "protesters". The federal judge over ruled them and the suit is going forward. E
I think what you'll find is that a specific course of action has never been and never will be legally prescribed. While San Jose may have had a duty to provide security or police staffing, the court won't rule on a specific course of action the officers there should have taken. As it relates to the Broward Coward the judge said he had a duty to act responsibly. I doubt the jury will find that he had a duty to walk into gunfire without a thorough assessment of the situation.