The lawsuit, filed in federal court on Wednesday, complained Ms. Bowser’s move, as well as her decision to rename a nearby street “Black Lives Matter Plaza,” came at the taxpayers’ expense but showed a preference for one faith — or belief — over others. The main argument in the 51-page complaint filed at the U.S. District Court for the District of Columbia is that Ms. Bowser is violating the Establishment Clause of the U.S. Constitution by supporting one orthodoxy over others. “The Black Lives Matter banner conveys that black people are the favored race of the city of DC, which...