Still, by now it ought to be clear that the best chance to protect what Mr. Obama calls “core U.S. security interests” lies in a victory for the Iranian opposition. That may look unlikely for now. But it is considerably more probable than a turn toward detente by those now engaged in murdering young women. There may not be much that can be done to help the opposition, though some tangible steps — more money for broadcasting into the country, for example — are readily available. But at the least, nothing should be done that would harm the cause of change. That is not just the moral course; it is the most pragmatic and realistic.