Saturday's nationwide "March Against Sharia," sponsored by a group known for aggressively criticizing Islam, has in recent days become a rallying cause for right-wing extremists, forcing march organizers to repudiate some of their own supporters and prompting concern about clashes with militant leftists. The marches, due to be held in at least 19 states, are being coordinated by ACT for America, a conservative grassroots organization that calls itself "the NRA of national security." The group has a long history of opposing Sharia, which is a legal or philosophical code derived from Islamic scripture and meant to guide the behavior of observant Muslims. The ACT for America organizers say an adherence to Sharia among Muslims leads to abuses against women, from discrimination to honor killings.