An American role is not likely to stop at the Mosul dam, where fighting reportedly resumed a day after Obama said Iraqi forces, with backup from American air power, had reclaimed it…

The second unintended consequence is that, after three years of avoiding intervention, the U.S. may have effectively crossed the threshold on Syria, because the Islamic State will be a threat to minorities and majorities across the region, as well as American interests, if the group holds any territory. The Islamic State controls almost a third of Syria. It has the oil-rich east and is now pushing toward Aleppo in the north and Damascus in the south. The Islamic State has slaughtered or threatened tribes and minorities in Syria too. Even if U.S. military muscle pushes it back into Syria, Islamic State forces remain a broader regional threat.