1) ISIS is bad. Their track record of repression against religious and ethnic minority groups in Iraq speaks for itself. So does their habit of executing Western hostages in lavishly produced videos. Rolling back their influence and destroying their organization are desirable outcomes.
2) ISIS is not in any clear way a direct threat to the lives of ordinary Americans. The murder of two American journalists working in a war zone is a cruel crime, but it's not a national security emergency. Innocent Americans are, unfortunately, murdered every day right here at home.
3) Defeating ISIS is not the top priority of anyone in the region. Bashar Assad's main goal is to hold power in Damascus. Iraqi Shiite factions' objective is to hold power in Baghdad. Turkey and the Gulf states want to check Iranian power, and are playing out a complex regional rivalry amongst themselves. Syria's "moderate" rebels are trying to avoid getting wiped out. Iraqi Kurds are continuing their decades-long quest for statehood.
4) The USA also has other fish to fry. We're not going to team up with Iran, Assad, and Hezbollah to wipe out ISIS by constructing a Teheran-led arc of Shiite-controlled polities sweeping from the Persian Gulf to the Mediterranean Sea. We are also not going to dispatch tens of thousands of American soldiers to serve as occupation forces in Mosul, Tal Afar, and other Sunni cities in Iraq.
5) Obama's actual plan for ISIS is a reasonable response to the circumstances. Regional diplomacy is a no-brainer. Air strikes against ISIS in Iraq will prevent it from overrunning any major new strategic targets and give other Iraqi factions breathing space to get their act together and go on the offensive. Air strikes in Syria will prevent ISIS from getting too comfortable. Attempting to aid non-ISIS rebel forces in Syria will, if nothing else, mollify our Arab partners and help encourage them to cut off the flow of money to ISIS.
6) It is extremely unlikely that this plan or anything resembling it will actually destroy ISIS. The basic problem is that as ISIS gets weaker, the incentives for regional actors to take anti-ISIS action gets weaker. Kurdistan, Iran, Saudi Arabia, Qatar, Syrian rebels, and Iraqi Shiites are all trying to accomplish very different things in the region. While ISIS is strong, it is perhaps possible to coordinate all or most of these actors in an anti-ISIS direction. But if ISIS is degraded, the will to prioritize anti-ISIS action will also degrade.
7) The biggest problem with Obama's current approach isn't what he's promising to do, but what he's promising to accomplish. Over the course of 2014, Obama's anti-ISIS statements have become increasingly dire and alarmist.
8) The shift in tone appears to have two causes. One is backlash to his ill-advised quip about ISIS being global jihad's JV team. The other is polling indicating that the American public was profoundly affected by the execution videos, which were the single most widely-noted news event since 2009.
9) Public opinion always matters in politics and therefore in policymaking, but the fact of the matter is that the American people have this a bit mixed up. The beheadings are not the most alarming thing ISIS did this summer (try taking Mosul or genocidal violence against religious minority groups) and the rise of ISIS isn't even the summer's most alarming foreign policy crisis (try Russia's invasion of Ukraine and apparent probing of Estonian and Finnish borders). There is no good reason for the United States to take maximal action against ISIS, not least because none of our potential partners in the region are going to.
10) Alarmist rhetoric and a policy of wise restraint make odd bedfellows. If the US catches some lucky breaks (or ISIS some bad ones) it may all work out for the best. But Obama's speeches are writing checks his policy can't necessarily cash. And eliminating ISIS' ability to occasionally kidnap westerners who travel into the conflict zone is much more difficult than eliminating its ability to capture new Iraqi cities or threaten major oil fields. If another shoe drops in a bad way, there is enormous risk that the president has set the country up for a cycle of unwise escalation.
11) "We will not get dragged into another ground war in Iraq," Obama promised last night. Certainly we shouldn't. But in the context of the administration's stated aspirations, this is more of a vague hope than anything else. If Obama really wants to stick to the policy he's outlined, he needs to find a more measured way to describe what he's promising it will achieve.