The Islamic State group's recent victories have called Barack Obama's Middle East strategy into question and once again made Iraq an issue on the US electoral battlefield.

It has been 12 years since president George W. Bush marched into an unpopular war in Iraq, and still the reverberations are being felt.

With militant jihadists in control of several major Iraqi cities, now including Ramadi, Republicans and Democrats are scrambling to assign -- and deflect -- blame.

Democrats say the former Republican president's ill-conceived and even more poorly managed overthrow of Saddam Hussein is the root cause of today's carnage.

Republicans counter that the incumbent Democratic president's blind determination to drawdown US troops in a conflict he never supported, has allowed Islamic State to thrive.

Many of the major candidates in both parties, from Hillary Clinton to Jeb Bush have struggled to reconcile past positions with today's received wisdom that the war was a mistake.

Burdened by politics and familial ties, 2016 Republican hopeful Bush needed multiple attempts to clarify a confused answer to whether he would have repeated his brother's actions.

Similarly tough taking Republican Marco Rubio whiffed, vaguely suggesting it was the right decision given the information Bush then had.

But the presumptive Democratic candidate Hillary Clinton is in a particularly tricky spot.

Her vote in favor of the Iraq war and her role, as Obama's Secretary of State, in forging current strategy mean she is tethered to the unpopular decisions of both the Bush and Obama administrations.

- 'Paying day-by-day' -

"I've made a mistake, plain and simple," she said in Iowa on Tuesday, addressing support for a war that arguably already cost her a shot at the White House in 2008, when she lost the party nomination to anti-war candidate Obama.

"That one vote is still there but further away," said Julian Zelizer a political historian at Princeton.

"More important will be how she deals with the record of the Obama administration."

And that record is also looking increasingly shaky.

A long-standing alliance with Israel is on the brink, Iraq, Syria, Libya and Yemen are in flames and everywhere tensions between Sunni and Shiite, secular and religious, democratic and authoritarian are spewing to the surface.

"We don't have a strategy at all," said Obama's former defense secretary and Clinton's cabinet colleague Robert Gates describing current Middle East policy. "We're basically sort of playing this day-to-day."

Obama's White House had hoped that 2015 would see things turn around, a deal with Iran could help slow Tehran's nuclear program and perhaps even its proclivity for supporting destabilizing proxy groups.

Through airstrikes, backing Kurdish fighters in northern Iraq and help for the country's military to get back on its feet, the White House had hoped to retake Mosul by the end of this year.

A victory in the "capital" of Islamic State's caliphate would allow a qualified declaration of victory and quiet damaging criticism heading into an election year.

Clinton will be hoping that the tide can still be turned but until then she, like other candidates, has ample reason to be anxious.

American political history is littered with the casualties of war.

In 1968, vice-president Hubert Humphrey's link to Lyndon Johnson's quagmire in Vietnam hamstrung his campaign and helped Republican Richard Nixon enter the White House.

Forty years later, John McCain's defense of Bush's actions in Iraq helped tip the balance in favor of Barack Obama.

Regardless of the outcome, what happens on the battle fields of Iraq looks like it might again influence what happens at ballot boxes across the United States.