ERIE, Pennsylvania - Donald Trump knew that J.D. Vance could take a punch. But during their first week together on the campaign trail, the former president wondered just how many hits his new running mate could absorb.

The volume and velocity of attacks from Democrats stunned even Trump. He was unaware of the most incendiary remarks that opponents were rapidly unearthing from Mr Vance’s past, and the former president told allies that he was troubled by the idea that more comments would come to light as Democrats savaged his heir apparent as weird and anti-women.

A month later, polls show that the number of Americans who dislike Mr Vance continues to grow – but Trump could not be happier.

The reason: Mr Vance’s relentless pace of full-throttle performances as Trump’s well-trained attack dog has pleased the former president and instilled a sense of stability inside a campaign still shaken by President Joe Biden’s sudden exit from the race.

Trump had instructed his young sidekick to fight forcefully through those initial attacks and later said Mr Vance’s execution exceeded his expectations, according to three allies who insisted on anonymity to discuss private conversations.

In a quintessentially Trumpian display of bravado, the former president has privately praised Mr Vance by comparing himself to Vince Lombardi, telling people that his eye for political talent was now on par with the Hall of Fame football coach’s ability to find Super Bowl-calibre players.

But beyond Mar-a-Lago, early returns on Mr Vance are less enthusiastic. Polls show that he effectively amplifies Trump’s political strengths but that he also magnifies his weaknesses. Mr Vance’s approval rating improved by nearly double digits among the nation’s least educated and poorest voters since joining the Republican ticket – but plunged by even wider margins among college graduates and independent women, according to an NPR/PBS News/Marist poll.

How those conflicting opinions either resolve themselves or become further inflamed will help determine whether Trump ends the race in less than 10 weeks with a second presidential term or a second electoral defeat.

“JD never had a honeymoon; he had a hurricane, but I think a lot of that is in the rearview mirror now,” said Mr Charlie Kirk, a Republican activist close to the Trump campaign. “He’s further animated the conservative base and also voters we are looking to run up the score with, which are white working-class voters and young male voters.”

Democrats, however, have been outraged and confounded by Mr Vance’s vice-presidential bid. In 2024, Trump had spoken at length about finding a running mate who was uniquely qualified to take over as president – and then picked Mr Vance, who assumed his first elected office just in 2023 and turned 40 less than a month ago.

The most damaging attack on Mr Vance in July centred on his comments from a Fox News interview in 2021, when he lamented the numerous “childless cat ladies” among American leaders, including Ms Kamala Harris.

Many voters shrug off similar comments from Trump because they view the 78-year-old former president as something of an elderly uncle “who doesn’t understand the world has changed”, said Mr Bill Kristol, who was the chief of staff for Vice-President Dan Quayle in the late 1980s and early 1990s.

“But Vance has gone out of his way to adopt a set of views from an ideological, right-wing milieu on things like child-rearing and how women should more or less stay home,” said Mr Kristol, an organiser of Republican Voters Against Trump. “That is harder to understand from someone who is 40.”

Mr Vance’s media strategy, allies said, functioned as his attempt to reach beyond the conservative base and to joust – carefully and respectfully, for the most part – with network anchors.

Mr Vance’s interactions with reporters produced one of his most effective days on the trail when he attacked his Democratic counterpart, Governor Tim Walz of Minnesota. The Harris campaign had posted an old video of Mr Walz pushing to restrict access to “weapons of war that I carried in war”. Mr Walz served 24 years in the military but never in combat.

Mr Vance and his team had been searching for some way to disrupt a streak of positive news for Ms Harris, who had unified her party around her nomination, and their tactic of highlighting the discrepancy worked. Cable networks broke into their coverage to report his criticisms of Mr Walz.

Some pundits concluded that the move had been designed by Mr Chris LaCivita, a senior Trump campaign adviser who had played a key role in similar “Swift Boat” attacks on Senator John Kerry, the 2004 Democratic nominee. But Mr Vance had anticipated the opportunity on his own and quickly seized it.

Later, when his plane followed Air Force Two into Chippewa Valley Regional Airport in Wisconsin, he hurried down the tarmac straight for Ms Harris’ plane.

Her motorcade sped off before Mr Vance could execute any publicity stunt, so he instead spent a few minutes with reporters who had gathered to see Ms Harris. He mostly mocked Ms Harris for not taking more questions, a criticism that remains a top talking point for Republicans.

“I just wanted to check out my future plane,” Mr Vance said when he returned to his motorcade.

Ms Harris’ campaign later posted a meme-style video on social media aimed at mocking Mr Vance. The clip shows her meeting Girl Scouts on the tarmac before quickly cutting to footage of Mr Vance’s arrival. A narrator says, “All of a sudden, I hear this agitating, grating voice.”

Mr Vance’s self-assured manner with the news media has reached the point where questions from reporters now account for about half of his typical 30-minute events. The rules are stacked in his favour.

Mr Vance seeks questions mostly from local outlets, which, by definition, are typically focused on regional issues. The news media is corralled at the back of the room, where the microphone is held by campaign staff members, limiting opportunities for follow-up questions.

“You all want to see me take some questions from the media?” Mr Vance asked a crowd inside a Wisconsin warehouse stacked with PVC products on Aug 28.

An approving roar erupted from the crowd.

But unscripted events carry risk, too. At a trucking logistics company in Pennsylvania, Mr Vance’s audience sustained a chorus of ear-splitting boos when a woman introduced herself as a reporter from CNN.

The next reporter stumbled on her question, and multiple audience members heckled her and loudly mimicked her stammer.

Mr Vance also overextended himself while speaking about a confrontation between Trump’s team and Arlington National Cemetery officials. Mr Vance angrily cursed Ms Harris for her response to the incident – but she has said nothing. Her campaign’s only reaction was from a spokesperson who offered a brief and largely unnoticed response to a question during a cable news interview.

“She wants to yell at Donald Trump because he showed up?” Mr Vance said to applause. “She can go to hell.” NYTIMES