India, Sept. 16 -- Seth Moulton stood on the House floor Tuesday and delivered the line that has become the unofficial epitaph for the administration's Iran policy. "Remember when Donald Trump said that this war would last just a few weeks?" the Massachusetts Democrat and Marine veteran asked. Six months later, the Congressional Budget Office has put a number on what those weeks have actually cost: $38.1 billion, and counting.

The House voted 220-204 to invoke war powers authority and order a halt to military operations in Iran, the third time members have taken that step this year, and the third time the effort is expected to die in the Senate. What made Tuesday different was the accumulation: the CBO's estimate landing on the same day...