We didn't have to INVADE Iraq.
Bush started withdrawing troops in 2007 and signed and agreement that we'd be out by the end of 2011. As that date approached, Iraq's Prime Minister al-Maliki refused Obama's request for an extension.
We installed a Democratically elected goverment. Sure, we invaded on a lie, but to call that gov't a lie and our agreement with them a lie and do what we want...? Maybe if Trump was President for those 16 years, sure. But otherwise, can't keep getting by on blatant lies. Plus Obama won largely on a mandate of getting us out of there, so there's that.
Officailly we wish for the ouster of Assad. But like the rest of the dictators in the region and elsewhere we officially dislike, they serve a purpose (most we put in power as well) by keeping things in control. Plus Syria was always Russia's foothold in the region, and they support President Assad, their puppet.
We went in to stop ISIL from taking over, taking credit for what the Kurds did for us, which included losing 11,000 fighting while we lost an entire 6, yes, SIX soldiers.
Russia is there for Assad, and Iran actually has more soldiers than Russia and the US in Syria, since they have a mutual defense pact with Assad.
Iran also has worked closely with the Kurds, and it was those two plus Iraqi Shiite militia who did most of the fighting to oust ISIL from Iraq that Trump takes credit for as well.
That's why we call Iran sponsors of terrorism - they've been unofficially doing our dirty work for us since the 1990s in the Balkans.