Recent polls have found deepening public aversion to U.S. military actions overseas after more than a decade of American involvement in Iraq and Afghanistan. Going back to Ronald Reagan’s surprise attack on Grenada in 1983, presidents have typically had at least a slim majority of the country on their side, with larger offensives, such as the 1990 Gulf War and the start of the war in Afghanistan in 2001, garnering significant public support.

In the case of Syria, public support for U.S. action appears especially weak. An NBC News poll last week found that just 42% of Americans backed the use of military force against the Syrian government over its alleged use of chemical weapons. That number rose to 50% if the action was limited to cruise-missile strikes from U.S. naval ships.

“There are real concerns about the efficacy of action and deep fears of U.S. entanglement in Syria,” said James Lindsay, a foreign-policy expert and former Clinton administration official. “The public has a clear case of intervention fatigue after 12 years of engagement overseas, the longest stretch in U.S. history.”

Studies of popular support for U.S. military action have found it hinges largely on three factors: perception of the stakes involved for U.S. national interests or security; the prospect for success; and the potential costs, financially or in U.S. casualties.