Gov. Greg Abbott on Thursday cleared state authorities to return migrants they apprehend to the border, setting up a potential clash with the federal government over the authority to enforce immigration law.Immigration law enforcement is a federal responsibility. Abbott appears to be testing the limits of state authority by empowering state law enforcement and National Guard troops under state deployment to bring migrants to the ports of entry — stopping short of using state resources to expel migrants from the country, as immigration hawks have increasingly called for in recent months.It was not immediately clear how state law enforcement would ...