Khánh , who had played a minor role in Diệm 's overthrow Change_of_leadership , joined Connect forces with Generals Trần Thiện Khiêm , Nguyễn Văn Thiệu , who felt Change_sentiment they deserved better posts in the junta , and Colonels Nguyễn Chánh Thi and Đỗ Mậu , the latter being the director of military security under Diệm and an effective strategist .