Sometimes, too, the military advice is not what the civilian hawks want to hear. Remember, the on-scene commanders in Iraq opposed the 2007 "surge" of troops.
Right now the administration is reportedly reconsidering what to do in Syria, and maybe moving toward creating some safe zones for civilians. Some anonymous sources suspect that the Pentagon is inflating the forces needed as a sign of resistance to the new policy. Let me tell you, that has often been the suspicion of civilian policymakers, as I've noted in much of my own research. While high projected costs are sometimes part of the bureaucratic politics, I believe the differences often derive from civilian naivete about military operations. "Surgical air strikes," for example, require suppression of enemy defenses and search and rescue capabilities along with the brave bombardiers.
In the case of Syria, the U.S. military has a long record of doubt regarding what limited measures could accomplish. At least the Times reporters mention this past history:
In a 2013 letter to Congress, General Martin E. Dempsey, then the chairman of the Joint Chiefs of Staff, said any military intervention in Syria would be an “act of war.” He estimated that establishing safe zones in Syria could cost more than $1 billion per month if American ground troops were used — even stationed outside Syria — to assist regional forces patrolling the zones.
If the warriors are reluctant, it's important to give their views very careful consideration.General Dempsey’s letter also signaled his skepticism about either humanitarian zones or a no-fly zone across all of Syria.