After listening to the administration’s case to Congress for military action against Syria, you get a better understanding of why some officials initially were reluctant to make it. The president has left the sales job to his secretary of state, and John Kerry has argued forcefully that we are morally and strategically compelled to intervene. The evidence of gas attacks and stocks of chemical weapons is irrefutable, the secretary says; vital U.S. interests are at risk; and we have to either check this rogue now or face a much more dangerous one later. Listening to Kerry, one can close one’s eyes and revisit the debates about Hitler, Vietnam and Iraq.

John Kerry Secretary of State John Kerry pauses before testifying before a House Foreign Affairs Committee hearing on Syria. (Carolyn Kaster/Associated Press)

But what is missing from this debate, as it was from the other war debates in history, is the “known unknown” of what military intervention will look like and what it will achieve. What will our cruise missiles target?  What does success in civil-war-torn Syria look like? The elimination of Syrian leader Bashar al-Assad’s chemical weapons, which appear to be widely distributed across his country? And how far are we willing to go to ensure success? What will we do if, as generally happens in war, things on the ground get worse and the generals ask for more options? On this question yesterday, Kerry equivocated, saying at first he thought it unwise to rule out using ground troops, but then, sensing the slipperiness of that slope, said he would “shut the door” on that option.

Mark Twain once said that a cat wouldn’t sit on a hot stove twice, but he wouldn’t sit on a cold one either. The American people seem to share this cautious sentiment after the misadventures in Iraq. Their doubts seems to center not on the moral case for intervention or even basic acceptance of the importance of U.S. leadership in the region. Rather, they want an answer no one can give them: Will U.S. intervention in Syria make things better or worse?