Analyzing strategic aspects of judicial decisionmaking is an important element in understanding how law develops. In this article, we examine sophisticated voting on the U.S. Supreme Court by empirically modeling justices' decisions to pass when it is their turn to vote during conference discussions. We argue that, due to the opinion assignment norm, the chief justice may pass when one of the key conditions necessary for sophisticated voting - certainty about the views held by other justices and the agenda - is lacking. By passing, the chief can view his colleagues' votes in order to determine which vote will allow him to assign the majority opinion and, ultimately, forward his policy preferences. Using data from Justice Lewis F. Powell's conference notes, we show that the chief passes for this purpose, and that doing so is an effective strategy. In addition, we show that the senior associate justice in a case, who has a nontrivial chance of assigning the majority opinion, also passes for strategic reasons. As we expect, the data indicate that the remaining associates seem not to pass for strategic purposes.