ANAMOSA, Iowa — As the Democratic presidential candidates fanned out across Iowa and New Hampshire on Thursday to address voters still scarred by President Trump’s victory in the 2016 election, Joseph R. Biden Jr. argued that any Democratic nominee would be vulnerable to baseless criticism and disinformation in the general election.

Mr. Biden’s remarks in Iowa, at his first political event of the 2020 election year, came a day after a deceptive video of him circulated online, highlighting how campaigns are still struggling to combat false information on the internet.

“You’re going to see a lot more of not only my statements being taken out of context and lied about or altered, you’re going to see whomever the Democratic nominee is, because that’s how this guy operates,” Mr. Biden said, adding that Democratic candidates would face unfair attacks from Mr. Trump “if I were to drop out of the race tomorrow” or “if I were to drop dead tomorrow.” (There was no evidence that the video was connected to the president.)

Mr. Biden’s comment came in response to an event attendee who asked him about his ability to beat Mr. Trump, and also to clarify his remarks in the video, which had been misleadingly edited to wrongly suggest that Mr. Biden was making racist remarks. In fact he was emphasizing the need to change “our culture” around violence toward women.