In the next few days, President Obama faces one of the most complex and far-reaching decisions of his six years in power.
It is a dilemma that goes to the heart of his Presidency, his power, and his promises to the American people.
And, ironically for the man who won the White House by opposing war in Iraq, the dilemma is about, yes, whether to fight a war in Iraq.
Does the White House look the other way as hardcore Islamist fighters take control of vast areas of the country?
Or does the Commander-in-Chief order US forces once more to fight in Iraq, re-igniting a war that he had promised the American people was over?
Allowing Sunni extremists to carve out a Syrian-Iraqi safe haven for their brand of militant Islam would be a disaster for the White House on many levels.
Quite apart from the civil war it is likely to trigger in Iraq, it would fatally undermine the President's claim that America has won the so-called 'war on terror' and can now focus on a period of peace and nation-building at home.
Already Obama's critics say the strategic neglect of Iraq is about to be followed by the abandonment of Afghanistan.
So the pressure is immense for the President to order US forces to reverse the stunning advances of ISIS, preferably before Iraq is overwhelmed by a three-way Kurdish-Sunni-Shiite bloodbath.
A US intervention would have to be conducted exclusively by air strikes.
The prospect of American ground troops fighting their way back into Mosul, Tikrit and Fallujah is impossible to contemplate for a country that has already paid such a catastrophic price in blood and treasure battling in those same far-away cities.
But can ISIS be defeated from the air? Can drone strikes or US fighter jets change the balance of power on the ground?
Above all, is America about to get sucked back into the same costly quagmire that haunted this country for a decade?
As the Pentagon debates the unpalatable options, at a minimum the Obama Administration is going to rush military aid to the beleaguered Shiite-dominated government in Baghdad.
In seeking to halt the threat of a sweeping victory by Sunni extremists, America will find itself on the same side as Iran's Revolutionary Guards and Syria's President Assad.
Chaos makes for the strangest of allies, and the toughest of dilemmas.