I think it is safe to say that none of the regional actors will be likely to invade CONUS (or Canada!) with conventional forces. So what? They can certainly destabilize the Middle East region even more than it is at present. Play out the scenario. The Coalition withdraws, the Kurds declare an independent state, Iran and Turkey attempt to intervene in "Kurdistan", Iran supports extremist Shi'ite groups in the south and centre of Iraq, Jordan and Saudi Arabia support a "Sunni Centre", Hezbollah attacks Israel on Iranian orders while Syria sits on the sidelines and picks up money, resources and territory from all players.
OK, you sort of got me up to here, though you haven't given a decent reason why Hizbullah would attack Israel at this juncture. It's not like American troops in Iraq exactly deterred them the last time.

Certainly you may have a MAD scenario for oil which might act to stop conventional destruction of the facilities, but that is irrelevant since the oil prices will rise anyway. Where else is the US going to get oil? From their good friend Chavez? From us (Canada - we're already the US's largest external supplier)?
Canada, Mexico, Saudi, Nigeria, Venezuela - same places we get them from now.

With a general conflagration in the middle east, oil prices start to exceed U$100/barrel and the American population demands that "something be done!". The Democrats, under General Pelosi, blame the Republicans for rising oil prices, poverty, lack of medical care to the general population, global climate change and demand an intervention to secure oil production facilities. Within 2 years of a pull out, the US military will be sent in again - by a Democrat President - in a blatant attempt to gain control of the oil fields so that Californian voters can drive their SUVs without screaming over the price of gas.
Fantasy. Do you consult for Newt Gingrich? If not, you should.

Meanwhile, in the Middle East, the bastard children of the Muslim Brotherhood (including al-Quaida) have "proven" to the world that the Great Satan and his Crusader minions have been expelled from the Muslim World. The Caliphate is proclaimed in Egypt (supported by Saudi Wahabis and Yemeni Mamelukes), and a global "jihad" is proclaimed. Europe, noting the obvious imperialist attitude of the United States, declares itself "neutral", once again blaming the Americans for having "no sense of history", and, by degrees, becomes an Islamist stronghold as the mobs of AQ inspired barbarians in Paris, Berlin and Amsterdam demand "equality", i.e. Sharia Law.
Utter delusion. Seriously Marc, were you mainlining whatever it is that Richard Perle and Mark Steyn have been smoking the past five years? A "caliphate" in Egypt? Right, because the NDP, Egyptian security services, and army would just step aside for the Egyptian MB --- which, as you know, hates al-Qaeda.

Also --- Yemeni Mamelukes?! Where can I buy my own slave soldiers? At least if you're going to proclaim an AQ "caliphate", be a little more realistic say al-Qaim or Ramadi, and if you're going to recall ahistorical figures from the medieval past, you might as well as be really ahistorical but super-cool, like "Wahabi Assassins, but with Ninja powers!"

As for the "Eurabia" fantasy --- seriously, where does this come from? Is the enormous 7% Muslim population in the Netherlands that close to overrunning the entire country? How about the gigantic 9% in France? Please.