MIDDLETOWN, Ohio -- Speaking at his first solo rally in his hometown of Middletown, Ohio, former President Donald Trump's running mate Sen. JD Vance attacked the Democratic Party over President Joe Biden stepping down as the party's nominee and getting behind Vice President Kamala Harris.

"If you want to run for president, you've got to make your case to voters. You make your case to voters," Vance said.

"[Trump] faced some good competition, and he made his case to voters," Vance later said.

Vance's rally came one week after he was announced as former President Donald Trump's running mate for the 2024 presidential election.

On Monday, Vance took center stage in his hometown, which has played a crucial role in his upbringing and was the catalyst for much of what has happened to him, including being the backdrop of his memoir, "Hillbilly Elegy," in which he shared his story of growing up in poverty in America's Rust Belt and being surrounded by violence and addiction.

The Ohio senator made his first official appearance at a campaign rally on Saturday in Grand Rapids, Michigan, alongside Trump. During that appearance, Vance wasted no time attacking Harris, who only one day later would receive an endorsement from Biden and other Democrats to top the Democratic ticket.

During the rally, Vance claimed, "elite Democrats got in a smoke-filled room and decided to throw Joe Biden overboard." Biden left the race amid mounting calls from fellow Democrats to do so since his poor debate performance last month.

"This is not OK, ladies and gentlemen. You cannot, for three-and-a-half years, take a guy who clearly didn't have the mental capacity to do the job," Vance said.

Vance then turned to Harris and Senate Democrats, repeating a claim Trump has made that she was complicit in hiding Biden's mental fitness.

"Kamala Harris lied about it. My Senate Democratic colleagues lied about it. The media lied about it," Vance said, adding it was an "insult to voters."

During his remarks, he said the Trump-Vance ticket would fight for different groups of people including workers, parents and grandmothers.

"What President Trump and I want to do -- we want to a drill, baby drill," Vance said. "We're gonna shut down that border, we're gonna put American citizens first, because that's what American citizens are gonna elect us to do. It's common sense."

Vance held his second campaign rally of the day in Radford, Virginia, where he continued his efforts to court voters while also taking aim at Biden, and Harris' new campaign.

"Now history will remember Joe Biden as not just a quitter, which he is, but one of the worst presidents of the United States of America," Vance said.

"But my friends, Kamala Harris is a million times worse and everybody knows it," Vance continued.

Escalating his attacks on Harris, Vance also claimed that the vice president was selected by "billionaires and Barack Obama and Nancy Pelosi" instead of Democratic voters -- while Trump won multiple cycles of Republican primaries -- calling the Democratic Party's actions a "threat to American democracy."

Multiple times throughout the remarks, Vance also shared his personal moments with Trump, including when Trump called him to offer him the vice presidential candidate position -- saying that he had initially missed the call.

When they eventually got on the call, Vance said Trump quipped, "JD, you just missed a very important phone call. Maybe I should offer it to somebody else."

Vance went on to bring up the assassination attempt made against Trump during his campaign rally in Pennsylvania on July 13.

"That's the President Trump I know -- the guy who stood in defiance of an assassin's bullet and then just a few moments later called for national calm and unity. And they say that he's mean-spirited. That's not the Donald Trump I know," Vance said.