In effect the Saudis are threatening to enter the Iraq war far more directly in order to challenge rising Iranian domination. They do so knowing they are risking a wider regional war, but also knowing that not only do both the U.S. and Israel support them but that in fact the U.S. and Israel may well want to foment a regional war in order to take down Iran.
From the article:
There is reason to believe that the Bush administration, despite domestic pressure, will heed Saudi Arabia's advice. Vice President Cheney's visit to Riyadh last week to discuss the situation (there were no other stops on his marathon journey) underlines the preeminence of Saudi Arabia in the region and its importance to U.S. strategy in Iraq. But if a phased troop withdrawal does begin, the violence will escalate dramatically. In this case, remaining on the sidelines would be unacceptable to Saudi Arabia. To turn a blind eye to the massacre of Iraqi Sunnis would be to abandon the principles upon which the kingdom was founded. It would undermine Saudi Arabia's credibility in the Sunni world and would be a capitulation to Iran's militarist actions in the region. To be sure, Saudi engagement in Iraq carries great risks -- it could spark a regional war. So be it: The consequences of inaction are far worse.