Self-described Democratic socialist Bernie Sanders, the 2020 presidential candidate who has long assailed America's growing income inequality, released 10 years of tax returns on Monday that confirm his newfound status as a millionaire.

The senator, who routinely rails against "millionaires and billionaires" and the "rigged" economic system that protects their standing, saw his income spike on royalties from sales of his book, "Our Revolution," published shortly after his 2016 race for the Democratic nomination.