Donald Trump’s vice-presidential pick JD Vance vowed in a primetime speech to fight for working-class Americans that he argued had been “cast aside and forgotten” by the Democrats.

Introducing himself to millions of Americans watching on TV at home, the Ohio senator channelled his humble roots in the Midwest as he assailed “career politicians” like President Joe Biden.

He argued in his address at the Republican National Convention in Milwaukee, Wisconsin, that Trump was the “last best hope” for Americans.

Trump and his running mate will challenge the Democratic White House ticket, currently Mr Biden and his Vice-President, Kamala Harris, in November’s election.

Mr Biden’s account on X, formerly Twitter, hit back at Mr Vance on Wednesday night, over his positions on abortion and Ukraine.

Mr Vance, 39, is hoping to become one of the youngest vice-presidents in US history.

In the speech, he charted his journey from a difficult childhood in small-town Ohio to the US Marines, Yale Law School, and finally the US Senate.

The author of best-selling memoir Hillbilly Elegy, about his impoverished family in Appalachian coal country, said “America’s ruling class” had destroyed communities like his hometown with trade agreements and foreign wars.

“From Iraq to Afghanistan, from the financial crisis to the Great Recession, from open borders to stagnating wages, the people who govern this country have failed and failed again,” he said.

He continued: “Donald Trump represents America’s last best hope to restore what – if lost – may never be found again.

“A country where a working-class boy, born far from the halls of power, can stand on this stage.”

The running mate, who is married to Usha Vance, a lawyer and daughter of Indian immigrants, said the US had traditionally welcomed newcomers, but that it ought not to import foreign labour.

“When we allow newcomers, we allow them on our terms,” he said.

Mr Vance was previously an opponent of Trump, once dismissing the Republican as an “idiot” who could become “America’s Hitler”.

But Mr Vance, who was by then working as a venture capitalist in Silicon Valley, later mended fences with Trump.

He won the former president’s endorsement and was elected to the Senate in 2022, taking office the following year.

Democrats have seized on some of Mr Vance’s past statements, including that he doesn’t “really care what happens to Ukraine” and support for a nationwide abortion ban.

He has recently moderated his stance on abortion to align with the official Republican platform, which says the issue should be decided by individual states.

He did not mention the war in Ukraine during his speech, or say much at all about foreign policy, which was the theme of the third day of the party conference.

Mr Vance did say that US allies must share in the burden of securing world peace and America would avoid conflict but “punch hard” if provoked under a second Trump presidency.

He began his speech by talking about last Saturday’s assassination attempt on Trump.

“They accused him of being a tyrant,” he said. “They said he must be stopped at all costs. But how did he respond? He called for national unity, for national calm.”

In the immediate aftermath of the attack, Mr Vance blamed it on Mr Biden’s rhetoric and his warnings that his Republican rival poses a threat to democracy.

Most Americans had little knowledge of him until Wedesday night.

A CNN poll conducted last month showed that 13% of registered voters said they had a favourable opinion of Mr Vance and 20% an unfavourable one – nearly two-thirds either had never heard of him or had no opinion.

Some convention-goers on Wednesday said they were still learning about his biography.

Cindy Dore and Jackie Canon, two Republican delegates from Louisiana, said they were excited by Trump’s pick.

“He’s young, vibrant,” Ms Dore said.

She said she appreciated Hillbilly Elegy, but other than that, she didn’t know a lot about Mr Vance.

The speeches began shortly after it was announced that President Biden had been diagnosed with Covid-19 and temporarily suspended campaign activities.

The climax of the Republican convention will be Donald Trump’s speech on Thursday night.

Chris Devine – an associate professor of politics at the University of Dayton and co-author of Do Running Mates Matter? – told the BBC that vice-presidential picks tend to have quite a small effect on the overall race.

“If it’s the case that people look at JD Vance and see him as insufficiently experienced, they will think less of Donald Trump and his judgement,” he says. “Not by a lot, but potentially on the margins.”

But Mr Devine also noted that Mr Vance is an “incredibly talented communicator” despite being a relative political newcomer.

Additional reporting by Kayla Epstein and Brandon Livesay