Democratic candidate Bernie Sanders has questioned Hillary Clinton's praise for Nancy Reagan as a leader in the early years of the AIDS pandemic.

“I just don't know what she was talking about,” Sanders said during an appearance Sunday on CNN's State of the Union.

During an interview Friday with MSNBC at Nancy Reagan's funeral, Clinton praised the former first lady's “very effective, low-key advocacy.”

“Because of both president and Mrs Reagan, in particular Mrs Reagan, we started a national conversation when before nobody would talk about it,” Clinton said.

Clinton owned the mistake, saying on Twitter that she had “misspoken” about the Reagans' record on HIV and AIDS. “For that, I'm sorry,” she wrote.

“In fact, that was a very tragic moment in modern American history,” Sanders said Sunday. “There were many, many people who were dying of AIDS. And in fact there was demand all over the country for President Reagan to start talking about this tragedy, and yet he refused to talk about it.”

Clinton offered a lengthier apology on Saturday, writing that she had said “something inaccurate when speaking about the Reagans' record on HIV and AIDS.”

“To be clear, the Reagans did not start a national conversation about HIV and AIDS. That distinction belongs to generations of brave lesbian, gay, bisexual and transgender people, along with straight allies, who started not just a conversation but a movement that continues to this day,” she wrote.

“I'm glad [Clinton] apologized,” Sander said, “but the truth is it was not President Reagan and Nancy Reagan who were leaders … quite the contrary … they didn't get involved in it.”