JD Vance, the Republican vice-presidential nominee, said on Sunday that he agreed with former President Donald J. Trump that some of his Democratic opponents posed a bigger threat to the United States than foreign adversaries.

Asked on NBC whether he agreed with Mr. Trump’s declarations that Democrats like Representatives Adam Schiff and Nancy Pelosi were more dangerous than adversaries like Russia and China, Mr. Vance supported his running mate.

“What he said, and I do agree with this, what he said is that the biggest threat we have in our country, it’s not a foreign adversary, because we can handle these guys,” he said. “We can handle foreign conflicts. We can’t handle — look, under Nancy Pelosi’s long life in public leadership, the United States has gone from the pre-eminent industrial power of the world to second next to China. That fundamentally belongs on Nancy Pelosi’s shoulders.”

And Mr. Vance, who appeared on Sunday morning news shows on CBS News, CNN and NBC News, sought to defend Mr. Trump against the recent warnings from several people who served in high-ranking roles in the Trump administration that the former president posed a threat to democracy.

John F. Kelly, the former Marine general who was Mr. Trump’s longest-serving chief of staff, said last week that Mr. Trump had praised Hitler and Hitler’s generals and met the definition of a fascist. And Gen. Mark A. Milley, the retired chairman of the Joint Chiefs of Staff, who was appointed by Mr. Trump, was quoted in Bob Woodward’s new book, “War,” calling Mr. Trump “fascist to the core.”

Mr. Vance sought to portray the former Trump administration officials who have criticized Mr. Trump as warmongers, or as bitter at having been fired.

And he downplayed the significance of Russia’s spreading disinformation in American elections, saying that it was bad but suggesting there was little the country could do about it.

On CNN, Mr. Vance was pressed on the threats that Mr. Trump has been making to political adversaries. Those threats include describing his opponents as an “enemy from within”; vowing to imprison people he deems to have “cheated” in elections, as he falsely accused Democrats and election officials of doing in 2020; and reposting calls on social media for specific Democrats and anti-Trump Republicans to be jailed or subjected to military tribunals.

“None of that sounds fascistic to you at all?” CNN’s Jake Tapper asked.

“No, of course it doesn’t,” Mr. Vance replied, denying that Mr. Trump had made some of the threats in question and saying that in other cases his words had been taken out of context.