For Lieberman and McCain, this history goes back to the siege of Sarajevo during the Bosnian war of the mid-1990s. The two senators joined Republican leader Bob Dole in pushing for U.S. intervention, against a resistant Pentagon and a reluctant President Bill Clinton. The Pentagon famously claimed that up to 400,000 troops would be needed to impose peace. When the United States and NATO finally bombed Serbian forces in the summer of 1995, the bloodshed ended in two weeks…

In some ways, the case for acting in Syria ought to be easier. It is not just a matter of preventing a humanitarian catastrophe, after all: The defeat of Assad would be “the biggest strategic setback for Iran in 20 years,” Central Command chief Gen. James N. Mattis told McCain in a Senate Armed Services committee hearing two weeks ago.

So far, however, facts and history haven’t helped much in the Syria debate. Instead, all sides are playing their usual roles. The Pentagon is talking about Syria’s allegedly formidable air defenses. Self-styled “realists” are claiming that helping the Syrian opposition will only inflame an incipient civil war. Obama is saying that “the best thing we can do” is to “unify” the “international community.” At times it seems nothing has changed since the Bosnia debate 17 years ago.