Sen. Bernie Sanders (I-Vt.) cannot help but defend Fidel Castro's communist regime in Cuba.

The self-avowed democratic socialist and frontrunner in the Democratic presidential race was given multiple opportunities both during and after the primary debate Tuesday to denounce the regime — instead he used both opportunities to defend his past comments in support of it.

Here's the quick background: Sanders was the subject of intense scrutiny in the lead up to the debate after his 1980s comments about Fidel Castro's Cuba were brought up in an interview on "60 Minutes" Sunday. In the interview, Sanders doubled down on his praise for Castro's "literacy program and said his campaign is "very opposed to the authoritarian nature of Cuba" but that "it's unfair to say that everything is bad."

During a CNN Town Hall the following day, Sanders once again refused to back down from his claims, saying, "truth is truth."

Fast forward to Tuesday night's debate where CBS moderators gave Sanders yet another chance to clarify his comments. Sanders, not taking the hint, dug his heels in again, this time to boos from the crowd.

"It's what Barack Obama said in terms of Cuba; that Cuba made progress on education," Sanders said as some in the audience booed.

"Really? Literacy programs are bad?" he asked in response to the boos. "What Barack Obama said is that they made great progress on education and health care."

But that's not all. CBS brought up the issue again in a post-debate interview with Sanders — this time with even more urgency. The interviewer highlighted the "potential political peril" that such views on Castro's Cuba could cause Democrats in Florida, a key swing-state, as he addressed Sanders' comments.

Slightly annoyed, Sanders yet again repeated essentially the same line.

"Cuba is a dictatorship, I've said that eight million times," the senator said, sounding exasperated. "But ... even under a dictatorship you can teach people to read and to write ... you could provide health care to all people."

Sanders' refusal to denounce the horrors of totalitarian socialist regimes like the one in Cuba under Fidel Castro has bewildered and angered Democratic pundits, who fear it will lead to the eventual re-election of President Donald Trump should Sanders become the nominee.

Even progressive CNN political analyst Van Jones couldn't believe what he heard from the leading candidate. Here was his reaction after last night's debate:

I was disappointed with Bernie's answer on the socialism question. He had to know that was coming. There's no reason to do a big retrospective nostalgia scream-fest about authoritarian regimes from the 70s. It was an opportunity for Bernie to clarify to the American people that when he says '"democratic socialism" — that's the point it's not that stuff from Cuba., it's not that stuff from the Soviet Union. It's the stuff you see in northern Europe that's working well for normal people and they vote all the time. He failed to do that. It's unbelievable he failed to do it. It's what a big chunk of our party needs to hear from him, and he didn't do it tonight.