Perhaps this is obvious, but I haven't heard anyone mentioning it, so I'll say it. The New York Times reports that during Cheney's visit to Riyadh the Saudis told Cheney that if the U.S. withdrew from Iraq it would back the Sunnis. Fine, but why summon Cheney to Riyadh to tell him that? They could have given the same message to the U.S. Ambassador or Condi Rice or any number of other people. Instead, they summoned the major White House advocate of the so-called '80% solution', a strategy whereby the U.S. would stay in Iraq but back the Shia, writing off meaningful Sunni participation in the government.
My guess is that there was another message sent -- one these reports aren't covering -- about what the consequences would be if the U.S. adopted such a strategy.