Mrs. Boxer helpfully detailed Democrats’ new strategy for getting a foothold. Now that cars are so much more fuel-efficient, she explained, the gas tax isn’t bringing in enough revenue to cover highway needs. How to fix this? Easy! Just replace the gas tax with a carbon tax.

As strategy goes, this is clever. The gas tax itself is unpopular, so Democrats are betting on some public support for killing it. They figure at least some Republican porksters will salivate at more state highway money. Democrats can initially sell the tax as limited to covering infrastructure, knowing that once the principle is established, they can ramp up. And all this can be silkily pitched as part of “tax reform.”

The only thing Mrs. Boxer did not explain was how the administration intends to balance this climate crackdown with its position atop an American energy renaissance. Mr. Obama spent the past election year bragging that gas and oil production had risen on his watch, hoping to cadge some credit for the economic boom that has accompanied private-sector drilling advances.

The administration has kept open the possibility of approving the Keystone XL pipeline.