The evidence is almost overwhelming.
Ignore hysterical Republicans' criticism of the UN. For all its faults, it helps over 100 million people every year; many would die without its help.
With low costs and low risks, a robust but still limited (no-boots-on-the-ground) U.S.-led intervention is the best hope for both the Syrian people and American interests.
While the spillover in Lebanon and Iraq is now the worst, U.S. inaction that allows current trends to continue threatens to destabilize U.S. allies including Turkey, Israel, and Jordan too.