In a CBS "60 Minutes" interview that aired Sunday night, Sanders was asked about his remarks on communism in the 1980s, when he contended that Cubans did not seek to overthrow the late communist leader because he "totally transformed the society." The self-described democratic socialist on Sunday, once again, pointed to social programs implemented by the dictator as a silver lining within his authoritarian government.
"We're very opposed to the authoritarian nature of Cuba, but you know, it's unfair to simply say everything is bad," he said. "You know? When Fidel Castro came into office, you know what he did? He had a massive literacy program. Is that a bad thing? Even though Fidel Castro did it?"
But responses to Sanders' comments already seem to be a preview of some of the searing attacks his competitors will likely unleash on him Tuesday night when the top seven candidates are expected to square off in another Democratic debate in Charleston, South Carolina.
"After four years of looking on in horror as Trump cozied up to dictators, we need a president who will be extremely clear in standing against regimes that violate human rights abroad. We can't risk nominating someone who doesn't recognize this," former South Bend, Indiana, Mayor Pete Buttigieg tweeted.
Former New York City Mayor Michael Bloomberg tweeted, "Fidel Castro left a dark legacy of forced labor camps, religious repression, widespread poverty, firing squads, and the murder of thousands of his own people. But sure, Bernie, let's talk about his literacy program."
Former Vice President Joe Biden's campaign echoed the other contenders, but went further.
"Make no mistake: Bernie Sanders' comments on Fidel Castro are a part of a larger pattern throughout his life to embrace autocratic leaders and governments across the globe," Biden's senior adviser Cristóbal Alex said in a statement. "His admiration for elements of Castro's dictatorship or at least willingness to look past Cuba’s human rights violations is not just dangerous, it is deeply offensive to the many people in Florida, New Jersey, and across the country that have fled political persecution and sought refuge in the United States. Bernie’s comments indicate he either fails to understand the pain and suffering that Fidel Castro, Nicolas Maduro, and Daniel Ortega have caused to so many people, including Americans now living here, or worse, that his ideology blinds him to the realities of life in these countries."
"We already have one president who praises dictators and their mob-like tendencies; we don’t need another one. As president, Joe Biden will stand up on the global stage against tyrants and fight for freedom and democracy," he added.
But the senator's campaign defended his comments by comparing Sanders to former President Barack Obama -- claiming that Sanders decries aspects of Castro's regime while lauding advances in others, such as education.
"Sen. Sanders has clearly and consistently criticized Fidel Castro's authoritarianism and condemned his human rights abuses, and he's simply echoing President Obama's acknowledgment that Cuba made progress, especially in education," said Sanders communication director Mike Casca, in a reference to Obama's 2016 remarks in Havana, when the president acknowledged the differences over "democracy and human rights," but added, "Cuba has made as a nation, its enormous achievements in education and in health care."
Obama's comments came during a historic visit to the island nation, marking the first time in nearly 90 years a sitting U.S. president visited Cuba, as his administration sought to restore diplomatic ties between the two countries. The trip occurred at the end of his second term, not in the middle of a heated primary race.
Sanders' comments could give the other presidential hopefuls -- eager to puncture his ascendant run after back-to-back wins in New Hampshire and Nevada -- ammunition to cast his platform as too liberal for a full Democratic ticket, just days before Saturday's South Carolina primary. It's the last of the early state contests before Super Tuesday brings the presidential contest onto a national map all at once.
The backlash against Sanders' remark was not only swift among the 2020 Democrats but also among a bipartisan slate of Florida lawmakers, a state that is home to the highest concentration of Cuban Americans in the country.
Rep. Debbie Mucarsel-Powell, D-Fla., excoriated Sanders for his comments on Castro. She is the first South American immigrant in Congress who represents a district that covers parts of Florida's southernmost tip, plus the Florida Keys, and encompasses "thousands" of Florida's Cuban population.
"I find Senator Bernie Sanders' comments on Castro's Cuba absolutely unacceptable," she wrote in a tweet. "The Castro regime murdered and jailed dissidents, and caused unspeakable harm to too many South Florida families. To this day, it remains an authoritarian regime that oppresses its people, subverts the free press, and stifles a free society."
Two other members of Florida's congressional delegation, Stephanie Murphy of the 7th Congressional District, which sits in the middle of the state, and Donna E. Shalala of south Florida's 27th Congressional District, condemned Sanders and signaled that he is out of touch with their constituents.
"@SenSanders comments on Fidel Castro are ill-informed & insulting to thousands of Floridians. Castro was a murderous dictator who oppressed his own people. His 'literacy program' wasn't altruistic; it was a cynical effort to spread his dangerous philosophy & consolidate power," Murphy tweeted.
"I'm hoping that in the future, Senator Sanders will take time to speak to some of my constituents before he decides to sing the praises of a murderous tyrant like Fidel Castro," Shalala said.
Despite Sanders winning 51% of the Latino bloc in Nevada, Shalala's and Murphy's responses both underscore the notion that Latino voters do not vote as a monolith and highlights the fear among a number of more moderate Democrats that a Sanders nomination could ultimately cripple the party down ballot.
Sanders' remarks are a flashpoint for the ongoing difficulties he presents to down-ballot candidates within his own party, who will have to grapple with his more liberal positions, such as "Medicare for All," while seeking re-election on potentially a different agenda.
House Majority Whip James Clyburn told ABC's "This Week" that if the Democrats nominate a socialist, it "would be a real burden for us in these states or congressional districts that we have to do well in."
"If you look at how well we did the last time, and look at the congressional districts, these were not liberal or what you might call progressive districts. These are basically moderate and conservative districts that we did well in, and in those districts, it's going to be tough to hold onto these jobs if you have to make the case for accepting a self-proclaimed democratic socialist," he added.
Freshman Rep. Joe Cunningham, D-S.C., whose district is hosting the 10th debate on Tuesday, told the Post and Courier, "South Carolinians don't want socialism. ... We want to know how you are going to get things done and how you are going to pay for them. Bernie's proposals to raise taxes on almost everyone is not something the Lowcountry wants and not something I'd ever support."
Earlier this month, Rep. Don Beyer, D-Va., the first House Democrat to endorse Buttigieg, sounded off on Democrats' apprehension to Sanders, telling ABC News, "They're terrified. ...Very few people see Bernie as electable."
But some Democrats remain confident in their down-ticket chances, regardless of the nominee, arguing that it is too early to know the Sanders effect on House members, who will likely run on their own brands.
On Monday, a Democratic strategist who works with House Democrats told ABC News, "I think we'll probably see more distancing if Sanders is the nominee for obvious reasons," before adding that on the whole, the most vulnerable members in the House are going to "have to define themselves."
But the strategist added, "It remains to be seen if he is the nominee if that upsets that 2018 model," which was rooted in defending the Affordable Care Act, protecting pre-existing conditions and running against Trump, and delivered House Democrats the majority.
ABC News' Benjamin Siegel and Adam Kelsey contributed reporting.