Was the Iraq War worth the costs in blood and treasure?

Tonight the last combat troops left Iraq and moved into Kuwait. The War lasted for 7½ years. We’ve spent a trillion dollars and lost 4.400 American lives. Nobody knows how many Iraqis died. We did not find weapons of mass destruction. The hints of Iraqi involvement in 9/11 used to gin up the war turned out to be false. We leave with the political situation in Iraq tenuous at best. There is no functioning government after inconclusive elections and a breakdown of negotiations to form a coalition government. The insurgency is beginning again.

What good have we we accomplished for long-term American interests? What harm have we done? Now, with 20/20 hindsight, was it worth it?