After weeks of speculation about who would get the nod to be Vice President Harris’s running mate, President Trump and his surrogates are trying out attacks against the new Democratic ticket now that the decision has been finalized.

Trump called into “Fox and Friends” Wednesday morning for his first interview since Ms. Harris announced that Governor Walz would be her running mate. When asked how he would “hone in” on how the two Democrats voted in the past, Trump called Mr. Walz a “smarter version of her,” comparing him to a popular Vermont senator, Bernie Sanders.

Trump touched on his signature issue, the border wall, saying of Mr. Walz that he’s for “no walls, no security, he’s worse than they are,” before saying, “This is a ticket that would want this country to go communist immediately, if not sooner.”

Trump also doubled down on saying that the ticket is “very insulting to Jewish people,” adding: “I think that any Jewish person who votes for a Democrat or in this case these people but who votes for a Democrat should have their head examined.”

Jewish Americans are among the most reliable demographics in their support of Democrats. In 2020, President Biden won 68 percent of the vote of Jewish Americans, while Trump won 30 percent.

Trump also attacked Ms. Harris, saying, “I hear she’s sort of a nasty person,” and, “I hear she hasn’t taken one interview.” He further attacked Ms. Harris by highlighting her past opposition to fracking, a position she’s since walked back, and claimed that she was “the original de-funder of the police.”

While Trump’s lines of attack Wednesday morning were more focused than his Tuesday musings on Truth Social, where he described a hypothetical plot by President Biden to retake the nomination at the Democratic National Convention, his campaign surrogates have leveled more specific attacks.

Mr. Vance, at a campaign stop at Philadelphia Tuesday night, criticized Democrats on border security, a top issue for Republicans and many independents.

“We know that every time Kamala Harris took an action to open the American southern border, it is families like many who stand behind me today who have suffered the most,” he said.

Mr. Vance also called Mr. Walz “one of the most far-left radicals in the entire United States government,” an attack Trump leveled against Mr. Biden in 2020 and in 2024 before he dropped out of the race.

Online, Trump’s campaign has been reviving talking points from 2020, circulating footage from the riots at Minneapolis that erupted after the murder of George Floyd by police. Mr. Walz hesitated to deploy the National Guard, waiting for three days. Trump, last week, also claimed that he was the one who deployed the National Guard to Minneapolis during the riots, even though it was Ms. Walz who signed the executive order.

“Tim Walz was the guy who let rioters burn down Minneapolis,” Mr. Vance says in a new video from the Trump campaign.

The new wave of Republican attacks come as some in the party are expressing concern that Trump and his campaign are not staying on message against their new opponent.

“This is what you would call a public nervous breakdown,” one Republican strategist and former Trump administration official, Matthew Bartlett, told Politico. “This is a guy who pummeled a semi-conscious president in a debate and literally out of a race. And now this is a guy who cannot come to grips with a competitive presidential race that would require discipline and effective messaging. And we’re seeing a candidate and a campaign absolutely melt down.”

Other Republicans, like the former leader of the Georgia GOP, John Watson, have also suggested that Trump should spend less time publicly expressing grievances about his loss in 2020.