Gary, Indiana (CNN) Sen. Bernie Sanders on Saturday rejected suggestions that his growing nest egg, mostly amassed from book sales following his 2016 campaign, undermines his political message.

"I didn't know that it was a crime to write a good book which turns out to be a bestseller," Sanders said at a community meeting in Gary, Indiana.

Since Sanders described himself as a millionaire earlier this week, he and his campaign have stressed that his policy platform, which is fiercely critical of "billionaires" and wealthy corporate interests, like private insurers and pharmaceutical companies, is unchanged. His Medicare for All push has been colored by relentless attacks on those industries.

"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 added, defiant and plainly frustrated by the line of questioning. "So again, I don't apologize for writing a book that was number three on the New York Times best seller, translated into five or six languages and that's that."

Sanders' place among the frontrunners in the 2020 Democratic presidential primary has invited new scrutiny, most of it directed at his finances -- and his tax returns, which he said last week would be released by Tax Day, April 15. Sanders made his 2014 tax returns public during his first presidential campaign, in 2016. This time he's pledged to share a decade of records.

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