It is not always clear whether readers are to see Pilate as a weak and indecisive figure or as a powerful and shrewd administrator (18:29–19:22). . . . Yet the appearance of weakness might be deceiving, since Pilate's actions finally serve Roman political interests quite well. He does not agree to crucify Jesus until the Jewish authorities reaffirm their loyalty to the emperor, and the sign Pilate puts above the cross simply calls Jesus the King of the Jews, which disturbs the Jewish leaders because it gives the impression that the Romans are executing an actual Jewish king. Pilate's refusal to change the sign suggests that the is quite content to give the impression that he is crucifying Jewish national aspirations along with Jesus. (Koester, The Word of Life, 72; my emphasis)
The irony, of course, is that Caiaphas sought to have Jesus executed in order to preserve the nation. But in Pilate's hands, the crucifixion of this supposed messianic pretender only further subjected the nation to Rome's power.