In 1987, the art of opera changed decisively. John Adams’s opera Nixon in China was so unlike the usual run of new operas in its concept that many people, on first hearing about it, assumed it had to be a joke of some sort. Turning the preposterous and reviled figures of Richard and Pat Nixon and Henry Kissinger into operatic heroes — they were all still alive in 1987 — seemed preposterously at odds with the dignity of the form.