Sen. Bernie Sanders (I., Vt.) remained vague Monday night about when he will release his tax returns.

When CNN town hall moderator Wolf Blitzer asked Sanders if he would release his tax returns as fellow candidate Sen. Elizabeth Warren (D., Mass.) decided to do, Sanders replied that he would, but offered no further response.

Blitzer pushed him on the question, asking Sanders "what was the delay?" and "why haven't you done that so far?"

"Well, you know, the delay is not—our tax returns will bore you to death," Sanders said. "There's nothing special about them. It just was a mechanical issue. We don't have accountants at home. My wife does most of it. We will get that stuff out."

"So, when do you think we will see your tax returns?" Blitzer asked.

"Sooner than later," Sanders said.

"What does that mean?" Blitzer asked.

"Soon," Sanders said.

Blitzer then asked Sanders if he was ready to release his tax returns.

"I think that we have to just do a few more little things, and check them out, but they're ready," Sanders said.

When Blitzer asked Sanders why he didn't release his tax returns when he ran in 2016, Sanders said he refrained because he did not win the Democratic nomination.

"I don't want to shock you, Wolf. They're very boring tax returns," Sanders said.

Sanders has recently come under fire for his frequent use of private jet travel, which stands at odds with both his positions on wealth inequality and on climate change. He has spent at least $342,000 on flights since the 2016 election, according to a report from Politico.

In the past, Sanders has come under fire for buying a $575,000 lake house in Vermont for summer vacations.