The White House is preparing a 90-day ban on diesel exports, a move almost everyone in the oil business says will backfire and push gas prices higher.

• Diesel prices are up 80% from a year ago, seven months into the Iran war, and a ban might shave only a few points off that.
• Refiners have to process a whole barrel to make diesel, so cutting diesel output means less gasoline too — and higher prices at the pump.
• Even the energy secretary said flatly that banning exports does not work, and Goldman Sachs warns gas prices would rise.
• Oil executives who funded Trump's campaign are breaking their silence to fight it, the one group that may still sway him.
• Europe gets hit hardest since the U.S. was its diesel supplier of last resort, with Russian and Iranian supply both off the table.

Outlook: The ban looks likely to go ahead as a midterm gamble, with the real damage — higher gas prices at home and a diesel shock abroad — landing by December.