Revolutions tend to devour their own, but rarely has this happened as swiftly, publicly, and predictably as it did with Portland’s overpraised “Wall of Moms.” The brainchild of a suburban Mexican-American woman named Beverly Barnum, the group was loosely organized among other moms on Facebook who were incensed that President Trump had dispatched federal officers to Portland to protect the federal courthouse that had become the main target of three-months-long protests in the city. Wearing yellow T-shirts and linking arms, the Moms created a “wall” between federal officers and Black Lives Matter protestors in July, chanting “Feds stay clear. Moms...