CONCORD, N.H. — A feud between Sen. Bernie Sanders and former vice president Joe Biden over Social Security escalated on Sunday, with Sanders directly attacking Biden's record but acknowledging that an anti-Biden video one of his aides promoted should have shown a fuller context of his rival's remarks.

The comments came a day after Biden accused Sanders (I-Vt.) of misrepresenting his record, prompting a sharp rebuttal from Sanders’s campaign aides but not the candidate himself. The growing dispute came amid polls showing Sanders and Biden at or near the top of the field in the early states with about two weeks left until the first voting takes place in Iowa.

Sanders also said Sunday he believes that gender is an obstacle for female presidential candidates, even as he continued to express the view that a woman can be elected president. Sanders and Sen. Elizabeth Warren (D-Mass.) have been engaged in a heated dispute over gender and electability, with both offering differing accounts of a private 2018 conversation on the matter.

On Social Security, Sanders was eager to speak about Biden’s record Sunday, something his aides have been encouraging him to do more frequently.

“I think anyone who looks at the vice president’s record understands that time after time after time, Joe has talked about the need to cut Social Security,” Sanders said in response to a question from The Washington Post as he left a radio interview here. “I don’t think that that is disputable.”

On Saturday, Biden claimed that a Sanders aide had been circulating video of his past remarks that Biden called a “doctored tape.” While that did not appear to be the case, fact-checkers have said the video was trimmed in a misleading way before Biden said he would protect those programs. The clip purported to show Biden praising former House speaker Paul D. Ryan (R-Wis.) and his proposals to cut Social Security, but Biden contended and fact-checkers agreed that he was mocking Ryan.

“I think there was a focus on one particular video,” said Sanders. “We should have the whole context.”

But Sanders defended his larger critique, adding, “You’re looking at one video.” He argued that it’s beyond debate that Biden has talked about cutting Social Security, pointing to Biden’s past support for a balanced-budget amendment that Sanders charged was hostile to the program.

Asked to respond, Biden campaign spokesman Andrew Bates called Biden “a champion of Social Security” with a 100 percent record of supporting Social Security as a senator from Delaware.

“We appreciate Sen. Sanders’s comments about the video his campaign circulated being taken out of context,” Bates said. “As Sen. Sanders himself said in 2015: ‘Joe Biden is a man who has devoted his entire life to public service and to the well-being of working families and the middle class.’ ”

Sanders said he has differences with Biden on a range of topics, including foreign policy and trade. “And I don’t think it is wrong to be talking about those issues,” Sanders said.

The Vermont senator, who has bounced back from a heart attack in October to rejoin the ranks of the race’s leaders, has also been in a tense conflict with Warren over the question of whether he said a woman can beat President Trump in November. Sanders was pressed on that topic in an interview with New Hampshire Public Radio on Sunday.

“Do you think that female candidates’ experience — have a different experience — running for president than you, and do you think that gender is still an obstacle for female politicians?” an interviewer asked him.

“The answer is yes. But I think everybody has their own sets of problems, all right?” Sanders replied. “I’m 78 years of age. That’s a problem. There are a lot of people who say, ‘Well, you know, I like Bernie, he’s a nice guy — but he’s 78 years of age.’ All right, so we have to argue: please look at the totality of who I am.”

In the interview, Sanders also said: “It is hard for me to imagine how anybody in the year 2020 could not believe that a woman could become president of the United States.”

Warren, asked about his remarks after a town hall at a public school in Des Moines that attracted about 500 people, said she would have “no further comment.”

She added: “I have been friends with Bernie for a long time. We work together on many, many issues. And that’s all I’m going to say on this.”