Congress is still scrambling to find ways to pay for its tax cut, so perhaps it should pay closer attention to last month’s news that George Soros had transferred $18 billion of his fortune to a private charity that he controls. There it will be sheltered from the Internal Revenue Service forever. This may be the single biggest tax dodge in U.S. history, yet no one on the right or left seems to have raised an eyebrow.

True tax reform is predicated on the principle that all income should be taxed at a low rate once, and only...