Bernie Sanders, the democratic socialist senator from Vermont who is known for his constant criticism of America's ultra-rich, has built quite the fortune for himself following the success of his three books. But he has insisted, once again, that his wealth does not undermine his political stance.

Speaking at a community meeting in Gary, Indiana, Sanders struck a defiant tone, telling those gathered, "I didn't know it was a crime to write a good book which turns out to be a bestseller."

Sanders recently claimed he was a millionaire (Source: Alex Edelman/Getty Images)

It's a stick he has been beaten with ever since he announced last week that he was a millionaire, a newfound status that he said will be confirmed when he releases 10 years of tax returns by Tax Day, April 15. But he and his team have both reiterated that this does not void his criticism of billionaires and wealthy corporate interests like private insurers and pharmaceutical companies.

"My view has always been that we need a progressive tax system which demands that the wealthiest people in this country finally start paying their fair share of taxes. If I make a lot of money, you make a lot of money, that is what I believe," Sanders said at the community meeting, according to CNN. "So again, I don't apologize for writing a book that was number three on the New York Times bestseller, translated into five or six languages and that's that."

Indeed, Sanders' book 'Our Revolution', which was published just one week after Donald Trump won the presidency, went on to sell 220,000 copies and claimed a spot on the Times' bestseller list. In fact, he's released a book every year since he lost the Democratic primary nomination to Hillary Clinton.

His 2017 book, 'Bernie Sanders guide to Political Revolution', sold an estimated 27,000 copies, while his most recent book, 'Where We Go From Here: Two Years in The Resistance', was published in November 2018 before he announced his intention to run for the Democratic nomination once again and has already sold 26,000 copies.

Sanders has insisted that his newfound wealth does not change his message (Source: Stephen Lam/Getty Images)

Forbes estimated that the sales of these three books have netted Sanders at least $1.7 million in royalties, but his campaign manager, Faiz Shakir, said the Vermont native still believes in "opportunity for all".

"The fact that he is somebody who has personally benefited from that opportunity is something that he feels should be a shared opportunity with everyone else," Shakir said. "He's made some money off a book. And I think that the opportunity that he has had is evaporating for so many others. He feels that strongly... There's nothing about any of these tax returns or the money or anything that'll come out that'll change that fundamental fact one bit."

In January, Sanders proposed that the government levy new taxes on "the wealthiest 0.2 percent of Americans" which would include a 45% tax on estates worth between $3.5 million and $10 million. Sanders' recent success as an author, as well as the fact that he owns three properties, could very well mean he finds himself on this list.