Here is a question to ask Hillary Clinton and Bernie Sanders: What is the best tax rate to impose on high-income earners to ensure there is enough government revenue to pay for your trillion-dollar promises to voters?

Perhaps they think it is 83%, a rate that economists Thomas Piketty and Emmanuel Saez hypothesized in 2014 in a widely circulated paper. Or maybe it is 90%, which Sen. Sanders told CNBC last May was not out of the question. “Our job is not to think small,” Mr. Sanders elaborated in the Huffington Post a month later. “It is to think big.”

Progressives have often reminded us that the U.S. had such rates in the past. From 1936 to 1980, the highest federal income-tax rate was never below 70%, and the top rate exceeded 90% from 1951 to 1963. Under Ronald Reagan, the top federal rate declined to 28% by 1988 and has never reached 40% since.

Read the full article at The Wall Street Journal: Hillary & Bernie, Tax Fantasists