The US never totally disengaged from Iraq when Obama withdrew the last of the "combat" troops. A large embassy and various business interests remained there. The embassy and related diplomatic missions had US military personnel providing security and the various business activities had their security contractors. Slightly over a month ago Obama began an escalation of US military participation in Iraq ostensibly in response to the threat faced by the Yazidi from ISIS. This involved more military advisers and "limited" air strikes. There was also mention of protecting other US interests in Iraq. The posture which he took at the time was that this was an intervention limited both in scope and time.
Last night Obama addressed the nation announcing an essentially open ended military escalation with the stated ultimate purpose of destroying ISIS. It is not limited in time and it isn't even clearly limited to Iraq since there is a suggestion of some type of involvement with the situation in Syria. The only clear constraint that he imposed was that there would not be US "combat" troops on the ground. Yet, he is increasing the number of military personnel on the ground as "advisers".
So what do we call this new military undertaking. Heaven forbid that anybody should call it a war. We haven't officially had one of those things since 1945. They have to be declared by congress. Since 1945 the US has become the dominant global military superpower that has intervened militarily in most parts of the globe at one time or another but we haven't been to war. We have a purposefully vague and unclear construction that attempts to address the relationship of the executive authority of the commander in chief and the power of congress. What happens in practice depends almost entirely on politics and the popularity of a given "military intervention". Nixon was forced out of office by a Democratic controlled congress over the issue of contempt of congress. Bush II enjoyed Republican control of both houses and public hysteria generated by 9/11. He could go to congress and get blank check authorizations.
Obama claims that he has the executive authority for the present undertaking without congressional approval, but he would like to have their support. The politics of this situation is about as muddy as it could possibly get. The Republicans are divided between traditional war hawks like McCain and Cheney who want another full invasion and libertarian isolationists like Rand Paul who question any form of military intervention. The Democrats are divided between party leaders like Pelosi who are prepared to support the president and progressives who are opposed to military intervention.
The Los Angeles Times comes up with a very plausible prediction of what will happen in congress at least until after the November election.
Congress expected to avoid vote on military action in Iraq, Syria
President Obama on Tuesday began a bid to convince congressional leaders — and the American people — of his strategy to defeat Islamic militants. But partisan divisions and political sensitivities in Congress make it unlikely lawmakers will agree on even a symbolic vote, much less exercise their legal authority to approve military action.
Congressional leaders, who were briefed at the White House before a planned prime-time presidential address Wednesday, have calculated that, with the midterm election just weeks away, lawmakers have little to gain from putting themselves on the record with a vote.
Despite rising public support for a muscular military posture, Americans remain weary after more than a decade of war — and although support for military action may prove unpopular, so might opposition.
Faced with the very real possibility that a growing coalition of antiwar Democrats and isolationist Republicans would defeat a resolution authorizing military force, most in Congress appear content to let the White House take the lead. Congress' failure to agree also could undermine the Pentagon and send a mixed message to U.S. allies and enemies abroad about American determination to defeat the Islamic State militant group.
Obama is basically giving congress an out with his assertion of executive authority. With that authority will go executive responsibility for the outcome. There is an immediate rise in public fear and hysteria that ISIS poses some kind of threat to the safety of the American public a la 9/11.
The New York Times has surveyed various security and intelligence analysts and reached the conclusion that the notion is not really plausible. Never the less Obama will get some credit for responding to public anxiety.
It looks like this situation will likely be in limbo for the next two months. The military steps that Obama is undertaking are unlikely to show conclusive results in that time. The outcome of the congressional elections could create a shift in the situation. Should the Republicans take control of the senate and retain the house they would likely become more assertive on various legislative matters. However, they are sharply divided on the issue of foreign military intervention. The likelihood is that we will just keep on muddling along.