Justice Powell wrote for the Court in eight opinions announced in June 1972. U. S. v. U. S. D. C., however, may have been the most important, and was certainly the most unexpected, particularly for President Nixon. (It was announced on June 19, 1972. Was Nixon’s reaction part of the 18 1/2 minute gap on the June 20th oval office recording? Unlikely, but we will never know.)
Less than a year earlier, citizen Powell had written an article for the Richmond Times-Dispatchthat included a vigorous defense of the “inherent power of the President” to wiretap without a court order in cases of national security. Here Justice Powell wrote for a unanimous Court in rejecting warrantless wiretaps in domestic security cases.
In Powell’s file for this case, you can read the research materials that may have changed his mind. You can also see how Justice Douglas convinced the Chief Justice to allow Powell to write this opinion.