Sanders would tax capital gains as ordinary income and eliminate opportunities under current law for avoiding the tax through gifts and bequests of appreciated property. Under Sanders, the top marginal tax rate on long-term gains and dividends would more than double to 64.2 percent from 23.8 percent, the report said.

Still Sanders, who describes himself as a Democratic socialist and is seeking the Democratic presidential nomination, would generate about 40 percent of his trillions in new revenue from broad-based plans that include levying an additional 2.2 percent income tax on all taxpayers; implementing a 6.2 percent payroll tax that would be paid by employers on all earnings; expanding the Social Security payroll tax to earnings over $250,000; and imposing higher rates on the highest incomes, the report said. Those taxes would pay for Sanders’s health-care program, which he says will cost $1.38 trillion a year.

“This is a very ambitious proposal,” Burman said. “Changes of this magnitude are going into uncharted territory.”