We went into Afghanistan to take down the Islamist leadership and decapitate Al Qaeda in the wake of a massive terrorist attack on our soil. We pretty much did that (although Al Qaeda's a hydra and hydrae are hard to decapitate), but we're still there cleaning up the mess.
We went into Iraq under the impression that Saddam Hussein still had chemical weapons (I say still, because we KNOW he used them on Iraqi Kurds some time before) in violation of half a dozen UN resolutions. We took him down, installed a new government, and stuck around a while to clean up the mess. (Incidentally, when the weapons weren't found, it was surmised that they went to Syria.)
While both operations accomplished the stated goals - eventually - it took time, effort, money, and blood. The time, effort, money, and blood were all called "wasted" by the Left, including our current President. You can agree or disagree with that, that's not the point.
The point is, if Iraq and Afghanistan were wastes of time, effort, money, and blood, even if they were "mistakes" as some Republicans called them, why are the people who made those pronouncements suddenly all in favor of doing the SAME THING to Syria for THE SAME REASON as it was done in Iraq?