Warren Would Take Billionaires Down a Few Billion Pegs

"I definitely understand how that would make lots and lots of extremely rich people uncomfortable," said Mr. Hanauer, co-founder of a Seattle-based venture capital firm and an early investor in Amazon. "But I'm more worried about our democracy."

"Don't get me wrong," he added. "I would prefer 3 percent." But even at 6 percent, he said, "we would all survive and continue to be rich and fly around in our planes."

He pointed out that most Americans had been living with meager income growth for decades, while the silk-thin layer at the top shoveled in enormous gains, cumulatively more than 400 percent since 1980.

"All you're doing is saying to the richest percent of Americans that the rate of growth of your assets and wealth will now match what has happened to other Americans over the last 40 years," Mr. Hanauer said.