The best thing for the US to do is to back off and tell its allies to do so as well.

The US cannot lead the Saudis and their coalition without a 90% risk of war with the Russian Federation.

If the Saudis go through with their coalition strike without US leadership, they will be utterly destroyed. They may even lose significant territory to Syria or Iran (I doubt Russia would directly control it) along with those oil resources. This would significantly diminish US+EU power as Russia would have an even bigger say in Europe's energy trade.