A campaign spokesman said Mr. Biden had previously drawn an analogy between an Obama assassination and the political killings of 1968 when speaking to younger audiences not alive at the time.
In 2008, running for the Democratic presidential nomination, Hillary Clinton drew criticism when she referenced the political assassinations of 1968 as she defended staying in the long primary battle against Mr. Obama. She noted first that Bill Clinton had not wrapped up the nomination until June 1992, and then added, “We all remember Bobby Kennedy was assassinated in June in California.”
At the event on Friday, Mr. Biden also recalled his early support for women’s rights, including the Equal Rights Amendment, and how he was he was sneered at for being on the edge of social change. He said critics had said, “Well, you know why Biden is for the E.R.A., he’s probably gay.”
But here’s the deal. An entire generation was energized. We finally finished the Voting Rights Act. We finally got the Civil Rights Act back on the road. We finally were in a position where we started to begin the women’s movement, and began to treat women — I remember because I was such a big supporter of the E.R.A in 1972, quote — to show you how things have changed, thank God — “Well, you know why Biden is for the E.R.A., he’s probably gay.” Not a joke.
Mr. Biden, the front-runner in the race for the Democratic presidential nomination, compared his political awakening in his 20s to the present moment, asking how many members of the audience, on the campus of Dartmouth College, were high school or college students.
About 40 hands went up in the audience of several hundred.
“Unless I’m mistaken, Donald Trump did for your generation what the loss of two of my heroes did for mine,” he told the students, adding, “What they did was make you realize, my God, we’re in trouble.”