Drupal 7 - Delete all of a content type
$node_types = array('congressperson');
// add the machine names of node types you want to bulk delete
$query = new EntityFieldQuery();
$query->entityCondition('entity_type', 'node')
->propertyCondition('type', $node_types, 'IN');
$result = $query->execute();
foreach($result['node'] as $node){
node_delete($node->nid);
}