PORTLAND, Ore. — No state is more emblematic of deepening political and cultural divisions in America than Oregon, where a movement is underway in the state’s more conservative southern and eastern counties to break away from the radically leftist urban centers in the northwest and become part of an enlarged Idaho.Such efforts have been around for decades as divisions sizzled under the surface. Each side sees the other with a growing contempt, as leftists in the state capitol, Salem, rule with a legislative supermajority and, increasingly, no regard for their neighbors in largely rural eastern Oregon. In that part of...