Trump said having JD Vance as his VP will have 'virtually no impact' on the race. Political scientists say otherwise.

• Donald Trump said vice presidents have 'virtually no impact' during a chaotic interview.
• Political scientists say otherwise, noting their influence on elections and governance.
• One said the selection of JD Vance Experts might even make some voters doubt Trump's judgment.

During a chaotic and sometimes combative interview at the National Association of Black Journalists conference on Wednesday, former President Donald Trump said vice presidents have "virtually no impact."

However, several political scientists told Business Insider they beg to differ, pointing out the significant roles running mates can play in both election-winning and governance.

Trump's remark was in response to a question about whether Sen. JD Vance, who appears to be the worst-polling vice presidential candidate in decades, would be "ready on day one" if elected.

"Historically, the vice president — in terms of the election — does not have any impact. I mean, virtually no impact," Trump said. "Historically, the choice of the vice president makes no difference. You're voting for the president."

While Trump praised Vance as "outstanding in every way," he did not directly answer the question.

This election may be an exception to the rule

"It is notable, for example, that he never really responded to questions about Senator Vance's readiness to take over the presidency," said Karen Hult, a professor of political science at Virginia Tech, in an email to Business Insider.

She noted that although elements of Trump's argument are correct — that, historically, vice-presidential nominees don't have a huge impact on elections — this is not always the case.

This race may buck the trend, Hult added, highlighting Trump's age, 78, and the attempted assassination attempt on him as factors that emphasize the "vulnerability of any single individual in office."

She said that this may heighten the significance of the vice-presidential candidate and their experience in the eyes of voters.

It can cast doubt on a presidential candidate's judgment

While home-state advantages and balancing the ticket can serve to boost a presidential ticket, a poor selection of a running mate can ultimately cost a candidate votes, said Christopher J. Devine, coauthor of the book "Do Running Mates Matter? The Influence of Vice Presidential Candidates in Presidential Elections."

"The choice of a running mate can influence voters by changing how they see the person running for president," he told BI.

"When voters come to doubt whether a running mate is up to the job, they blame the presidential candidate who picked him or her," he added. "That can actually cost the ticket votes."

In Trump's case, choosing a freshman senator over more experienced candidates might "hurt perceptions of Trump's judgment and cost him votes in the end," he said.

While it is impossible to know exactly how many votes it could cost a candidate, or Trump specifically, Joel Goldstein, a professor at Saint Louis University who has written books on the vice presidency, said that even a small number of lost votes could swing a close election.

"Many of our presidential elections are very close," he said, explaining that concerns over Vance's inexperience and a string of gaffes could make "a marginal difference in a competitive state" that could ultimately be decisive in the path to 270.

A heartbeat away from power

In Trump's remark asserting that vice presidents have virtually no impact, the former president also said, "You're not voting that way. You're voting for the president. You're voting for me."

Andrew Gelman, a professor of political science at Columbia University, told BI this isn't the case.

"When you vote, you're voting for the whole ticket," Gelman said.

Vice presidents are, after all, only a heartbeat away from the top job. Nine of the 49 vice presidents in US history — nearly one in five — have unexpectedly ascended to the presidency due to death or resignation.

Running mates serve a vital and impactful role on the campaign trail, said Richard Yon, the author of "Emerging from the Shadows: Vice Presidential Influence in the Modern Era."

He said that they act as "attack dogs" on behalf of the presidential candidate and work to drum up support for them.

For those who do become vice president, history shows they can play a meaningful role in governing. Yon pointed to examples such as Clinton-Gore, Mondale-Carter, Cheney-Bush, and Biden-Obama.

"All of these examples show that when they got into office, they really worked as partners, alleviating some of the president's responsibilities and, as a result, having an influential role," he said.

In response to Trump's comments, Yon said, "To do a blanket statement that the vice president or vice presidential candidate doesn't matter isn't taking into consideration some of the nuances that we've seen over the course of our history."