(CNN) "Soon."

That is the response Sen. Bernie Sanders and his presidential campaign have repeatedly offered in response to questions about when he will release his personal tax returns.

"Sooner than later" is what Sanders told Wolf Blitzer at a CNN town hall in February, just a few days after he launched his bid for the 2020 Democratic presidential nomination. Faiz Shakir, Sanders' 2020 campaign manager, told reporters about the same during a briefing last month.

Sanders has yet to release his tax returns, and his campaign has not explained the process in any more precise detail, even as Sanders has repeatedly said that there is nothing revelatory or interesting about his financial situation. But the pressure to disclose is mounting as his Democratic primary opponents begin to release their own. Sen. Elizabeth Warren has put out a decade of returns and has challenged other candidates to do the same.

"I put the past 10 years of my federal tax returns online," Warren tweeted on February 13, shortly before Sanders entered the race. "And now I'm calling on every other candidate for President to do exactly the same thing." She has also posted an online petition calling "on everyone running for president to release their tax returns."

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