For Migrants Headed North, the Things They Carried to the EndStrong political art is hard to make. So when it turns up, it’s worth a look. In an era of “great, great walls” and “bad hombres,” an exhibition called “State of Exception/Estado de Excepción” at Parsons School of Design fills the bill. It starts with a kind of special-effects installation, a video of what looks like fast-flowing river projected across the gallery floor and surging toward you. You walk over it to enter the show, and the shuddering current makes you feel woozy, as if you don’t quite know what your feet are doing.