Mayor Bill de Blasio of New York drew anger on Thursday by suggesting that many African-American voters supported former Vice President Joseph R. Biden Jr. because his record had not been sufficiently examined beyond his connection to former President Barack Obama.

Asked why Senator Bernie Sanders of Vermont lost decisively to Mr. Biden among black voters in recent races for the Democratic presidential nomination, Mr. de Blasio suggested those voters did not know enough about Mr. Biden — remarks that some called offensive and condescending.

“It stands to reason if people have a certain amount of information — and I don’t blame them for this, I understand it,” Mr. de Blasio said on the MSNBC show “Morning Joe,” before a host, Elise Jordan, interrupted.

“So you’re saying they were low information?” she asked.

“No, no, no,” said Mr. de Blasio, who endorsed Mr. Sanders in February. “I’m saying you had a whole lot of candidates, which I think is a very different discussion. The information that I think people received about Joe Biden was some of his historic connection, which, understandably, means something to people.”