I am thinking an oil and gold spike, crash in the stock market, and the possibility of additional global attacks in retaliation. Iran would have no reason not to furnish jihadists more effective weapons. If the Russian built reactor is damaged and delays payment, look for Russia to do to the US what we did to them in Afghanistan – furnish Man Portable Air Defense systems. Afghanistan will become untenable if our jets and helicopters become regular targets.
The worst case scenario is that Israel uses one of their tactical nukes and blames the fallout on Iran’s nuclear program. Israel could expect very limited success at some of the re-enforced enrichment facilities without troupes on the ground. The re-enforced enrichment facilities in Iran are long distance, and difficult targets for Israel.
Any outcome crashes the markets, hurts US war effort, and drives precious metal through the roof.