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Since President Obama ordered the U.S. military back into action in Iraq on Thursday night, his decision has brought scorn from frustrated hawks who disdain the plan's limited scope and hand-wringing from doves worried about mission creep. Both are right to be concerned because this is only Act I, with the rest of Obama's script still to be written.

Obama, caught flat-footed by the rapid advance of Islamist State extremists, is scrambling to reconcile conflicting objectives.

In the short term, he must blunt the immediate threat posed by the advancing ISIS forces. For that purpose, small-scale attacks should be sufficient. They can protect religious refugees fleeing an ISIS genocide and shield Americans in Iraq.

Even so, they cannot, for now, be so potent that they let Iraqis believe America will solve their problems for them.

U.S. efforts to force out Prime Minister Nouri al-Maliki, the author of this crisis, and form a new government to take on ISIS appear on the cusp of success — perhaps as soon as Monday — and should not be undermined.

The plan is a necessary first step — for reasons that should be obvious to critics on both flanks.

No one — including even the most extreme hawks — advocates reintroducing U.S. ground forces into Iraq. But to think ISIS will be dislodged by air power alone — as the hawks imply — is delusional.

ISIS is formidably armed with captured U.S. weapons, and its forces are led by highly trained officers who deserted Iraq's army in disgust with Maliki. It is flush with cash from captured oil, and its success is drawing a steady supply of fresh recruits, including Europeans and Americans.

If Iraqis — particularly Sunnis now supporting ISIS out off fear of Maliki — don't turn against it, the mission creep that the doves fear will be unavoidable because the threat to the U.S. is extreme.

Even with Maliki gone, the political task ahead is daunting. Months will be needed to unite the country's fractious factions. But as soon as possible, Obama must face the ISIS threat directly.

In a weekend interview with New York Times columnist Thomas Friedman, Obama said, "We're not going to let them create some caliphate through Syria and Iraq." And indeed, he cannot. The threat posed by ISIS is neither abstract nor confined to Iraq, as the doves seem to pretend.

ISIS' desire to strike the United States is unequivocal, and left unmolested it will eventually acquire the means.

To some eyes, it is already a greater threat than al-Qaeda, and Obama should treat it in the same uncompromising way.

That will require aggressive use of air power to deplete ISIS, rapid arming of Iraq's Kurds, who have proved to be reliable allies throughout America's misbegotten adventures in Iraq, and prolonged targeting of ISIS leaders.

On Saturday, Obama said this will be "a long-term project."

That is not what Americans fed up with Iraq want to hear. But this round of conflict is not about invading Iraq to uncover non-existent weapons of mass destruction, nor is it about naive ambitions of building a U.S.-style democracy in the Middle East.

It is about protecting the security of the United States.

USA TODAY's editorial opinions are decided by its Editorial Board, separate from the news staff. Most editorials are coupled with an opposing view — a unique USA TODAY feature.