ABC News coverage of shoot down of Syrian fighter/bomber by U.S. Navy F-18:
ABC Breaking News
Good analysis about potential messages and effects begins about 1:24. Did the U.S. draw that "red line" about what behavior it will tolerate? How will Russian leadership (read "Putin") respond? Will this lead to a "tit for tat" response attempt by Syrians (w Russian backing) or will the Russians respond directly?
"Self-defense" of coalition partners would seem to be a pretty reasonable rationale for the action the U.S. took.
But really, this is one of those middle of the meter reading on the "Degrees of Seriousness" meter.