Thanks to a quirky proposed surcharge, Americans who earn more than $1 million in taxable income would trigger an extra 6 percent tax on the next $200,000 they earn—a complicated change that effectively creates a new, unannounced tax bracket of 45.6 percent.

It hasn’t been advertised by Republicans, who have described their plan as maintaining the current top tax rate of 39.6 percent. And it goes against decades of GOP orthodoxy that raising taxes on the rich discourages work and reduces economic growth. Reached by phone, Steve Moore, a tax expert at The Heritage Foundation, said the surcharge was news to him. “I was just in a briefing with the White House on this,” he said. “They didn’t mention that. It seems kind of bizarre to me.”