“At the end of the day, however, removing Assad may not be doable at a price the United States is willing to pay,” the analysts write. “Although the Obama administration has for months called for Assad to go, every policy option to remove him is flawed, and some could even make the situation worse — seemingly a recipe for inaction.”

The authors say they examined a U.S invasion because if Washington is determined to stop the slaughter of innocent civilians, “an invasion may well be the only way to do so — it is certainly the only way that would be guaranteed to do so.”

“An invasion and the early months of an occupation would require 200,000 to 300,000 troops to be done properly,” the analysts write. “That alone should put the bill for a Syrian invasion at around $200 to $300 billion per year for as long as that number of troops would have to remain.