When Jagdish Chadha, a Kenyan of Indian extraction, decided in 1974 to fight his impending deportation, he unwittingly stumbled into one of the most far-reaching separation-of-powers battles of this century. In 1983, when the United States Supreme Court ruled in his favor, it effectively threw out hundreds of laws--more laws than it had overturned in its entire previous history--including acts that dealt with war powers, arms sales, and a host of...