Senator Elizabeth Warren is pushing a wealth-tax plan on the presidential campaign trail. She is promising that her tax would counter a rigged political system and raise enough money to pay for universal child care, a Green New Deal, student-loan relief, Medicare for All, and more housing subsidies.

Warren’s tax would be an annual levy of 2 percent on “net wealth” — meaning wealth minus debt — above $50 million and 3 percent on net wealth above $1 billion.

Wealth-tax supporters do not seem concerned about the likely damage to economic growth. But they should know that from a practical standpoint, wealth taxes in other countries have raised little money and have been a beast to administer.