Saudi Arabia is so concerned about the damage that the conflict in Iraq is doing across the region that it basically summoned Vice President Cheney for talks over the weekend, according to U.S. officials and foreign diplomats. The visit was originally portrayed as U.S. outreach to its oil-rich Arab ally.The thing about imperial relationships is that they're inherently two-way: Sure, you're appointed puppet can't afford to piss you off too badly, but just as importantly you can't afford to lose your puppet - you never know if you'll find a suitable replacement.
Nouri al-Maliki, theoretically the Prime Minister of Iraq, hasn't been able to convince the Americans of his value, so there's some talk of replacing him. But if the Americans arrange a coup at this point, it's almost guaranteed to see Moqtada al-Sadr take control. His militia now outnumbers the nominal Army of Iraq, so it's a definite possibility.
So not only does Maliki have to support the US, the US has to support him. Till death do they part.