US used the right tool for the job with cruise missiles, so they did not endanger their pilots and aircraft against the Russian S300 and S400 SAM systems. The use of a MOAB would risk aircraft and also cause unnecessary civilian casualties due to the wide blast effect. It is very important that the West keep the moral high ground compared to Assad's and Putin's war crimes.
The cruise missiles only carry 1000lb warheads, so dropping 58 of them will damage not obliterate an airfield. This was the point of the exercise. If Assad uses gas again and continues with his indiscriminate barrel bombing of civilians, grain stores, bakeries and hospitals like he did again yesterday, then don't be surprised if the next batch of cruise missiles are much closer to his palace. Legally, the US would have to be at war with Assad to use decapitation, so this is unlikely. Their targeting of terrorist leaders can and is classed as legitimate self defense, but it does have its critics. This could not be used as a reason against Assad as his and Russian forces have not deliberately and directly attacked any Western forces. This is also why we quite rightly warned Syria and Russia before the airfield attack, so they could evacuate their forces.
Legitimate preemptive nuclear strikes can be used by the US for their or their allies self-defense, something that Kim Jong-un might yet find out to his cost.
Obummer tried to get this option removed from US nuclear doctrine, but failed, primarily over North Korea and also for the protection of South Korea, Taiwan and Japan.
