1. Be careful about letting Congress off the hook for declaring war as a condition of using military force. Look what is happening here now: Members of the same Congress that never authorized anyone to conduct a military operation in Syria are complaining that President Trump is pulling those 2,000 troops OUT of Syria. If you're suggesting that these troops should be left there simply because it's "water under the bridge," then let's just dispense with Congress and let the President and a military junta run the damn country.
2. A declaration of war is a formality by definition. There's a reason for this: It is legal proceeding as much as anything else, and is accompanied by all kinds of legal formalities that govern everyone who is involved (diplomatic ties, military operations, prisoners of war, etc.). It also means the President of the United States must act as commander in chief to defeat an actual ENEMY -- which is the main reason why Congress will NOT declare war (the U.S. is not fighting an enemy in any of these actions; we're taking sides in civil wars).
3. Turkey may not be a great ally, but as fellow NATO members the U.S. and Turkey have mutual defense obligations to each other. That's probably the perfect definition of an "ally" in international affairs. A mutual defense obligation, however, does not obligate Turkey to assist a U.S. military campaign against a country that never attacked the U.S. If you want to make the case that Turkey and the U.S. no longer have mutual defense interests, then let's work on getting them out of NATO so they can be treated like any other Islamic dump over there.
4. The U.S. pulled out of Iraq at the end of 2011 because that's when the U.S. and Iraq agreed to have all U.S. combat troops leave Iraq. You can read the U.S.-Iraq Status of Forces agreement signed by George W. Bush in 2008 for the details.
5. Needlessly pissing away thousands of lives and hundreds of billions of dollars isn't a smart way to "learn from mistakes." I'm not sure why anyone would believe this line of thinking makes any sense. "We didn't do it right before, but you must let us try it again somewhere else."
6. Why do so many Freepers keep posting things that suggest countries like Russia and Iran are hostile occupying forces in Syria? They'll stay there as long as the Syrians want them there. What "leverage" are we supposed to have there? How about we send a family of Mexicans to move into your house when you're away for a few days -- just so they have "leverage" to make you call your Congressman to get the whole neighborhood turned into Section 8 housing?
7. If 2,000 U.S. troops in Syria are the only thing keeping the region from descending into chaos, then I'm go out on a limb here and suggest that the region isn't about to descend into any more chaos than it's already facing.