Jihadis are great at scream and leap tactics, especially when the targets have shaky morale. ISIL scared the Iraqi security forces out of Mosul and much of Iraq by using fear. But trained soldiers can rip apart jihadis who try to hold ground.
Our few special forces and intelligence agents backed by air power smashed the Taliban army in 2001. The French used a tiny military force to blitz their way through the jihadis controlling northern Mali last year.
The Iraqis probably don't have that military capability, unless their counter-terrorism forces are capable of fighting as formed units. That's probably a waste of their capabilities even if they could do it. We don't treat 30 SEALs as a really good platoon of infantry, now do we?
We could organize the general purpose Iraqi units for a plodding assault north. But it will be ugly even if successful.
We need a core of a mobile offensive force that can shatter the jihadis by moving north and calling down precision fire to smash up the jihadis as they try to defend their newly won caliphate.
Could Jordan provide a mechanized force to drive across the main highway from Jordan to Fallujah?
With our forces already deployed in Jordan in support of the Jordanian troops and our air power providing the hammer, could we break up a good part of the new caliphate in Anbar?
I've hoped that the Kurds might provide a similar force to spearhead the Iraqi drive north from the Baghdad region. But might the Jordanian provide this force, too?
Jordan could certainly be a target for destabilization by ISIL if the jihadis aren't defeated. Jordan may want to strike first. We might want to help Jordan.
UPDATE: Secretary Kerry is trying to get the Kurds to commit to Iraq's defense. It's either unlikely or the Kurds are bargaining, apparently.
Keeping the Kurds in Iraq is probably key to keeping Sunnis interested in staying in Iraq. The Sunni Arabs can at least think of allying with the Kurds to counter the Shia majority that will be split among factions in parliamentary maneuvering. Neither the Sunni Arabs nor Kurds could get majorities, but they could be kingmakers in the balance.
But if the Kurds leave Iraq, the Sunni Arabs are all by their lonesome with nobody else to look to for help. In that case they are likely to want to leave, too.
Then we'll see the joys of a partitioned Iraq.
UPDATE: I somehow neglected to note that during the 1980s war with Iran, Iraqi troops ultimately relied on firepower and sufficient discipline to slaughter far larger attacks by human waves of Shia jihadi--the Basij cannon fodder volunteers in the Revolutionary Guard Corps (Pasdaran). Iraqis can beat jihadis in far larger numbers than ISIL deploys if the Iraqis have the organization and weapons to do the killing.