Imagine Bush had not invaded Iraq in 2003 while Saddam toppled by Shiite Iraqis in some variation of Arab Spring which played out in Middle East in recent years. Imagine Iraq was presided by the same disastrous rule of Al-Maliki driving the country to precipice upon receiving blows after blows from IS coming from adjacent failed state of Syria which America never invaded. In that scenario, to what an extent Americans will be clamoring President Obama to intervene in Syria and Iraq? Al-Maliki essentially ripped out fragile stability purchased on backs of America's sacrifices in Iraq; and that Americans, especially Conservatives, want to restore back that scrambled egg - Iraqi stability. Americans feel obliged to retain fruits of their sacrifices. There is a feeling of squandering of that hard fought stability in Iraq. But Republicans and Hawks conveniently forget that whatever semblance of stability achieved it was because of the "pottery barn rule" - that Bush needlessly invaded Iraq and hence the responsibility came to USA in investing blood and treasury in Iraq to achieve peace. You remove that ill-fated decision in the first place and then one suddenly starts understanding remoteness of fight against IS and why it should not be America's sole responsibility to manage Iraq or for that matter to manage whole bunch of territories in this violent world. (One can very easily understand how Republicans would want to make the battle for Mosul as referendum on Obama Foreign policy; same way the battle for Kobani became test for Obama.)
As Greame Wood has argued in The Atlantic, the path on which IS has embarked upon - a literal interpretation of Kuran in an attempt to run Caliphate in 21st century; it can only end in one way: complete collapse of IS. The non-sustainability aspects of IS in today's world are simply too glaring, too many. How do you run a state today with no passport, no borders and no viable legal framework to honor property and contractual rights so as Capitalism can flourish in that state? Apart from these contradictory precepts IS wanting to adopt in today's world when rest of the world simply has no interest in accepting any of this non-sense; IS is simply creating too many enemies too fast to survive. Practically every other alternating interpretation of Kuran is unacceptable to IS resulting in a state which is permanently at war. No state in human history has survived which is permanently at war. This is especially true when resources at disposal of IS are paltry while all other competing forces are endowed with manifold resources. At some point, greater Ummah is also going to realize the nihilism insisted by IS and just the sheer survival instinct for those groups will start making them to work in ending IS. Shiite and Iran will have to confront IS for survival. Same goes for Wahhabi Islam of Saudi Arabia, Erdogon's Turkey and Kurds. Given this array of forces aligned against IS, question is why would America portray battle to capture Masul as Crusade? That is the "trap" American Conservatives want President Obama to enter into. They are framing this debate in same old Bush line of argument - "in order to save America here, you fight these terrorists there".
President Obama's failure is he is not making these things clear to Americans while more and more Americans get pulled into jingoistic case of owning the war against IS fully. In other words, he is letting his political opponents to set this debate as "to love America means to commit America's men & women" in the war theater of Iraq and Syria against IS. No one is talking here stopping active help by America in defeating IS. More needs to be done to bring together all those local and indigenous rivals of IS to finish it off. But America does not need to get involved in the vortex of IS ground fighting on the very first pretext. IS wants Crusade and it would love to have American foot soldiers in the battle. (Imagine a propaganda value it would unleash if it takes an American soldier as a prisoner of war with endless confessions on Internet...) Job of American leadership, contrary to the harakiri what these Republicans are advocating, is to avoid all these temptations and help natural, local forces to pull down IS.
Danger of other rogue attacks from terrorists outside the orbit of IS is ever present. Obama Administration needs to guard America from this danger. America needs to work with rest of the world in removing one of the cardinal causes giving rise to nihilism of IS - lack of governance and failed states. From Libya to Egypt, Iraq, Afghanistan, Pakistan, Bangladesh, Sudan, Nigeria; all these Islamic states are hobbled by governance failure. Those failures are the ones which are giving rise to an interpretation of Kuran which provokes these societies to opt for culture of death as propounded by IS. America's interest lies in working on these longer term objectives while not wasting all precious resources on IS when IS will collapse due to its own contradictions and everyone else as its enemy.