The good news is that the United States and the other four permanent veto-wielding members of the UN Security Council (China, France, Russia, and the United Kingdom) have at long last agreed on a resolution that would inflict a new round of sanctions on Iran to persuade its rulers to give up nuclear enrichment and their apparent pursuit of nuclear weapons. The bad news is that there is nothing in recent history that suggests that modest sanctions such as those contained in the draft resolution (the fourth in a series) will divert Iran's current leaders from their current path.
This is not to suggest that this new step is meaningless. The fact that Iran, abetted by non-permanent Security Council members Brazil and Turkey, has spent much of the last week trying to derail this diplomatic effort with an alternative plan (one that would have Iran send some of its enriched uranium out of the country without requiring it to stop enriching) suggests that Iran did not want this new UN resolution to pass. What matters as much or more than the new sanctions themselves is the unhappiness of Iran's leaders with their country being put in the global penalty box for all to see.
If and when this resolution is passed by a divided Security Council, the United States will then likely propose additional sanctions aimed at Iran's dominant Revolutionary Guards, something selected countries in Europe and beyond are prepared to embrace. Alas, such sanctions (along with even more muscular ones being developed in the U.S. Congress) also will probably fail to achieve their stated purpose.
So absent a change of heart -- or better yet a change of government in Tehran -- the world will soon reach the long-predicted fork in the road: an Israeli or American decision to undertake a potentially risky and costly preventive military strike on Iranian nuclear installations, or an Israeli and American decision to carry out a potentially risky and costly policy of living with an Iranian nuclear weapon (or something close to it) through a mixture of deterrence and defense. And when we reach that fork in the road, as the strategist Yogi Berra once advised, we should take it.