Washington(CNN) Sen. Bernie Sanders said Tuesday he's a millionaire -- which will be confirmed when he releases 10 years of tax returns in the coming days.
The Democratic presidential candidate made no apologies for his growing nest egg; in an interview with The New York Times, he said, "I wrote a best-selling book. If you write a best-selling book, you can be a millionaire, too."
The details of how Sanders became a millionaire will come to light when he releases his tax returns. Campaign manager Faiz Shakir told CNN Sanders' returns will be made public "on or before" Monday, the tax filing deadline for 2018.
The Vermont independent has repeatedly promised to release the information "soon." On Tuesday, Shakir said, "It will be done before the tax filing date is over. To my perspective, that is soon. I appreciate that there's been a lot of concerns that have been raised by a number of people but this will soon be over."
The release will likely quiet a growing din of concern over the release of Sanders' tax returns, which are expected to reflect an increase to his income through the sales of his book. But the unveiling will also open up Sanders, who released a single year of returns during the last campaign, to increased scrutiny -- the kind befitting his frontrunner status in this increasingly competitive and crowded Democratic primary field.
Speaking to CNN, Shakir said that Sanders "believes in opportunity for all, and 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. 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."
"Particularly as you get into future generations of Americans, it's less likely that somebody with little income could become a millionaire," Shakir added. "That is an ethic I think that truly does guide him. 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."
Sanders' book, "Our Revolution," was released in November 2016, a week after Donald Trump won the presidency. It claimed a spot on The New York Times' bestseller list. The book is about his bid for the presidency and the grassroots movement he worked to create while running against, and ultimately losing to, Hillary Clinton for the Democratic nomination.
His most recent book, "Where We Go from Here: Two Years in the Resistance," was published in November 2018 and outlines the blueprint for his 2020 presidential run. Sanders entered the race in February.
Sanders, who has been pressed on a timetable for his taxes everywhere from the halls of Congress to the airwaves of Comedy Central, now plans to turn the focus on Trump, who has never made public his own. Trump's acting chief of staff, Mick Mulvaney, recently said congressional Democrats -- who have formally requested them from the Internal Revenue Service -- will "never" see Trump's returns.
"Hey Mr. Trump," Sanders said after pledging on "The Daily Show" to releasing a decade of returns, "do the same thing."
During his interview with the Times, Sanders pushed back on comparisons between himself and the President.
"Not being a billionaire, not having investments in Saudi Arabia, wherever he has investments, all over the world, mine will be a little bit more boring," he said.