A possible path ahead is to take advantage of the post election negotiations and configure a leadership that accommodates Sunni interests. This would by necessity mean someone other than Maliki becoming Prime Minister.
Someone (possibly an American, but I doubt we are that knowledgeable, coordinated, or competent) needs to talk with key Sunni tribal leaders and former Army leaders—to include former Baathists. Just finding interlocutors who can represent and make commitments for those with legitimate interests will be difficult.
Maybe a UN representative could do this, but it would be better (essential) if such discussions were completely confidential. Bear in mind that anyone representing the Sunni voices will be at risk of assassination from ISIS. The vast majority of Iraqi Sunnis are secular (recall the Baathists and the Army under the former regime were strictly secular). The radical Islamists of ISIS will know they are small in number and, while ruthless, they can be crushed by the other Sunni’s when the time is right.
Maliki needs to know that the US will not support him as Prime Minister and the new government must accommodate Sunni interests in a material way. Stitching something together will be extraordinarily difficult. The last thing we should do is to give more military support to Maliki at this point. We would be seen as supporting the Shia side in what is becoming a sectarian war.
Somebody needs to talk to Sunni leaders and fast. At a minimum, they need to know that the US will not oppose them (and indeed should support them) so long as their goals are limited and realistic. They need to know that the US does not support Maliki, but does support a balance of power between Sunni and Shia groups.
The alternative to this path is to let the conflict play out. That will be costly, unpredictable, and end with a divided Iraq. Iran will be supporting the Shia in the south and others will back Sunni groups. Baghdad could look like Beirut in the 70’s, or worse.
We may wind up there anyway.