The US has evoked trade retaliation from Europe with a program most Americans would be shocked to learn involved international commerce. The affair shows how governmental meddling in energy markets yields perverse consequences. There will be other such lessons.US taxpayers US subsidize biodiesel—a methyl ester made from agricultural materials—with a tax credit of $1/gal and mandates. They believe doing so supplements fuel supply and helps the environment. Those who bother to check the numbers probably derive satisfaction from reports that their country produced 700 million gal of biodiesel last year, tiny though that volume is relative to total diesel consumption.But how many ...