As you've likely already seen, the US tonight launched a significant aerial attack on targets in Syria. The AP reports that about 60 Tomahawk missiles fired from warships in the Mediterranean Sea struck a Syrian air force base.
A key question will be the fate of Russian military and/or civilian personnel in Syria, which have become closely integrated with Syrian regime military personnel in recent years. Obviously Russian lives are no more important than Syrian lives. But the geopolitical consequences of Russian casualties or fatalities could be severe.