JD Vance formally accepted the Republican vice-presidential nomination on Wednesday with a deliberate, and at times divisive, pitch to re-elect Donald Trump in November.

Addressing delegates in Milwaukee on the third night of the convention, Vance, the junior senator of Ohio, presented the Republican party as a champion of working-class Americans while denouncing Democrats as out of touch and ineffective. The populist-tinged rhetoric offered the latest sign of how Trump has reshaped the Republican party and rejected much of the traditional conservatism of its past.

“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,” Vance told the energized crowd. “That is, of course, until a guy named Donald J Trump came along. President Trump represents America’s last, best hope to restore what, if lost, may never be found again.”

Vance leaned into his own personal story, first shared in his bestselling and controversial memoir Hillbilly Elegy, to bolster his message. He recounted experiences with childhood poverty in Middletown, Ohio, and his later acceptance to Yale Law School as he introduced himself to a much larger audience of Americans for the first time. In an emotional moment, Vance acknowledged his mother in the crowd and celebrated her 10 years of sobriety after decades of struggling with drug addiction.

With a mention of the battleground states that could determine the outcome of the election, he vowed that a Trump-Vance administration would deliver economic opportunity for working-class communities.

“In Michigan, Wisconsin, Pennsylvania and Ohio and every corner of our nation, I promise you this: I will be a vice-president who never forgets where he came from,” Vance said. “And every single day for the next four years, when I walk into that White House to help President Trump, I will be doing it for you, for your family, for your future and for this great country.”

Democrats scoffed at Vance’s attempt to appeal to working Americans, accusing him of backing “an economic agenda that will raise costs on American families, while giving billionaires and corporations tax cuts”.

Michael Tyler, communications director of the Biden campaign, added, “JD Vance is unprepared, unqualified and willing to do anything Donald Trump demands.”

In his speech, Vance joined the scores of Republican lawmakers who have condemned the assassination attempt against Trump on Saturday. Vance urged Americans to unify in the face of violence, even as he vilified Democrats who previously criticized Trump.

“I want all Americans to go and watch the video of a would-be assassin coming a quarter of an inch from taking his life,” Vance said. “Consider the lies they told you about Donald Trump, and then look at that photo of him defiant, fist in the air. When Donald Trump rose to his feet in that Pennsylvania field, all of America stood with him.”

In another sign of Trump’s takeover of the Republican party, Vance echoed the former president’s “America first” approach to foreign policy. Since joining the Senate last year, Vance has become one of the most outspoken critics of US aid to Ukraine and he doubled down on that isolationist stance in his speech.

“Together we will make sure our allies share in the burden of securing world peace – no more free rides,” Vance said. “We will put the citizens of America first, whatever the color of their skin. We will, in short, make America great again.”

The selection of Vance has unsettled some Republican lawmakers who embrace America’s active role on the global stage, and his speech underscored how Trump’s re-election could fundamentally reshape the relationship between the US and its European allies at a perilous moment. One senior European diplomat told the Guardian that Trump’s choice of running-mate was “terrible news” for Ukraine, adding, “[Vance] is not our ally.”

Nodding at the ideological differences within his party, Vance encouraged Republicans to engage in a robust debate over key policy issues.

“Shouldn’t we be governed by a party that is unafraid to debate ideas and come to the best solution?” Vance said. “That’s the Republican party of the next four years, united in our love for this country and committed to free speech and the open exchange of ideas.”

Voters will determine in November if that Republican party will indeed have the opportunity to govern for the next four years.