This article is a good explanation of the causes of the current fighting. It suggests to me that it would not have helped if the USA remained and continued to support al-Maliki. It also suggests that fighting off ISIS will not resolve the ongoing Shiite-Sunni conflict, an inclusive government that ends discrimination is requried.
"...The groundwork for today's problems began almost as soon as that last American convoy left in 2011. Sunni lawmakers protested the rounding up of many of their aides and security guards, and the country's vice president -- top Sunni leader Tariq al-Hashimi -- faced arrest and later fled the country.
The government of Prime Minister Nouri al-Maliki was supposed to usher in a political era of inclusion and reconciliation. His critics say those first days after the American departure were a signal of opposite intentions that have continued to this day.
The Sunni minority that had ruled Iraq via the iron fist of Saddam Hussein was at the political and social mercy of al-Maliki's Shia-dominated government. Today, they say, "inclusiveness" never materialized, Sunnis have been marginalized and resentment has festered in a divide-and-conquer political climate. As one local put it, "It's like if you're against us, you're a terrorist and we'll arrest you."
Why Iraq is in turmoil
This resentment, aided by the violent government shutdown of Sunni protest camps, provided an opening for the al Qaeda-linked Islamic State of Iraq and Syria (ISIS) to move into the Sunni heartland of Anbar Province in force. Al Qaeda is a beast that feasts on discontent and in Anbar there is no shortage of sustenance....
In 2006 the Americans convinced -- and paid -- Sunni tribal and religious leaders to fight the hardliners, with great success. But Sunni grievances never went away and some in Anbar see ISIS as comrades-in-arms against an al-Maliki government viewed as an oppressor of Sunnis. Other Sunnis see al-Maliki as the lesser of two evils -- they don't like how they're treated, but like even less the ISIS brand of hard-line, brutal "governance".
Al-Maliki has more than once termed the various fights and stand-offs in Ramadi and Fallujah as a fight against "al Qaeda", but it's not that simple.
The Sunni sense of being under the heel of a sectarian government, of being cut out of the running of their country, failing to share in growing oil revenues, has nothing to do with al Qaeda and won't evaporate once ISIS is forced from Ramadi and Fallujah.
The Americans aren't coming back to help out with boots on the ground, but they are giving other support -- offering drones, missiles, aircraft and other assistance.
But this isn't a battle to be won militarily. Sunnis -- many of whom have yet to get used to no longer running the country -- say they want to be part of the system that was meant to be "inclusive" but has, they feel, been anything but..........."
Inside Iraq: Two years after U.S. withdrawal, are things worse than ever? - CNN.com