The moderator gave Sanders an opportunity to disavow his past praise for Castro, but the Vermont senator declined to do so.
"What that was about was saying that the United States was wrong to try to invade Cuba, that the United States was wrong to try to support people to overthrow the Nicaraguan government," Sanders said.
Asked whether he regretted praising Castro, Sanders, a self-termed democratic socialist, avoided the question and reiterated that the key question was whether or not the United States should be pushing for regime change in foreign countries.
"Cuba is, of course, an authoritarian, undemocratic country and I hope very much, as soon as possible, it becomes a democratic country," Sanders said.