Obama did not have to do those things because Congress gave the Executive branch an Authorization to Use Military Force....
Congress gave that authorization to BUSH after he WRNT BEFORE CONGRESS AND ASKED FOR THAT AUTHORIZATION.
The NOBEL PEACE PRIZE WINNER never went before Congress and explained, like Bush did, WHE he wanted to take the nation to war.
The reason he probably chose not to is because he knew there is no way Congress would have given Obama authorization the authority to go to war with the intention of HELPING TERRORISTS - Al Qaeda - who slaughtered 3,000 Americans on 9/11/01, murder the President of a sovereign nation who was helping the coalition FIGHT Against terrorists and giving control of that nation to Al Qaeda.
The reason he probably chose not to is because he knew there is no way Congress would have given Obama authorization the authority to go to war, in the case of INVADING SYRIA, an International WAR CRIME of invading a sovereign nation without any reason to do so, without being requested or given permission to do so by that nation's leader.
And you are still asking why OBAMA did not take our troops out of Afghanistan? Why did he not only INVADE but also leave our troops in Syria?
As has been explained to you, no authorization was necessary.
We have been under a "National Emergency" and every year, each administration continues that emergency with an executive order.
The Bush administration did it. The Obama administration did it. The Trump administration did it. They are all the same.
It has to do with suspending the normal Constitution and enabling Continuity of Operations. That is why no War for drone strikes and military operations, assassinations, false flags, kidnappings, etc. has to be authorized. IOW, fascism. We have been a police state since Sept. of 2001.
Continuity of Operations - Wikipedia
Bush's extension from 2007;
For Immediate Release
Office of the Press Secretary
May 9, 2007
National Security and Homeland Security Presidential Directive
NATIONAL SECURITY PRESIDENTIAL DIRECTIVE/NSPD 51
HOMELAND SECURITY PRESIDENTIAL DIRECTIVE/HSPD-20
NSPD-51: National Continuity Policy
. . and they have been signed each and every September since, for if the executive didn't, it would give Congress an opportunity to reassert the Constitutional authority of the people.
Here's one from 2014;
Federal Register :: Continuation of the National Emergency With Respect to Certain Terrorist Attacks
2017;
Federal Register :: Continuation of the National Emergency With Respect to Certain Terrorist Attacks
Oh hey, look, one from Trump, guess he doesn't have to declare war anywhere he wants to bomb, kidnap, assassinate, false flag, etc. either;
Notice Regarding the Continuation of the National Emergency with Respect to Certain Terrorist Attacks | The White House
You do remember what the STATE deems "terrorist," right? Any damn thing they want.