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GRAND RAPIDS, Mich. — Vice presidential nominee JD Vance slammed his Democratic counterpart Kamala Harris on Saturday, asking Michigan supporters "what the hell" she has ever done and noting his own service as a U.S. Marine.

The swipe came as Vance and former President Donald Trump addressed voters at their first joint campaign event as running mates, and the first rally since a would-be assassin tried, but failed, to take Trump's life last week.

Thousands piled into the Van Andel Arena, home to the Grand Rapids Griffins hockey team, to see the pair, who are coming off a packed week at the Republican National Convention (RNC) in Milwaukee, where each accepted their respective nominations to appear on the GOP ticket together.

"I find it hard to believe that a week ago an assassin tried to take Donald Trump's life, and now we have this crowd in Michigan to welcome him back," Vance said after taking the stage.

WATCH: THOUSANDS DESCEND ON MICHIGAN TOWN FOR FIRST TRUMP RALLY SINCE FAILED ASSASSINATION ATTEMPT

Trump and Vance clapping

Former President and 2024 presidential nominee Donald Trump with Sen. and vice presidential nominee JD Vance, attend their first campaign rally together at Van Andel Arena in Grand Rapids, Mich., on Saturday. (Jim Watson/AFP via Getty Images)

He quickly began taking shots at Vice President Kamala Harris: "I've served in the United States Marine Corps … What the hell have you done?"

"What has she done other than collect a check from her political offices?" he asked, before going on to talk about his grandmother, who he calls "Mamaw," and his upbringing.

Harris ripped Vance after his Wednesday speech at the RNC in which he accepted his role on the 2024 ticket.

"It was compelling. It’s a compelling story. But it’s not the full story," Harris said after Vance's RNC speech. "Frankly, what is very telling is what he did not talk about on that stage. He did not talk about Project 2025, the 900-page blueprint for a second term. He did not talk about it because their plans are extreme, and they are divisive."

Vance later spoke to rallygoers about the various challenges facing the nation under President Biden's administration, including the fentanyl crisis, the border crisis and the economy.

RNC DELEGATES, GUESTS MAKE PREDICTIONS ABOUT BIDEN'S POLITICAL FUTURE AMID REPORTS HE MIGHT EXIT 2024 RACE

Vance clapping

Republican vice presidential candidate, Sen. JD Vance, R-Ohio, arrives at a campaign rally at the Van Andel Arena on Saturday, in Grand Rapids, Mich. (Anna Moneymaker/Getty Images)

Trump took the stage after Vance, beginning his speech by saying that he "shouldn't be here right now, but something very, something very special happened." He took a moment to recognize the supporters who were injured or killed at the rally last week.

"We continue to pray for the recovery of the two citizens who were wounded in that evil attack – David Dutch and James Copenhaver, two really incredible people," the Republican frontrunner said. "We remain in contact and send our deepest respect to the families."

Trump also acknowledged the death of Corey Comparatore, calling him a "hero" for protecting his family from the bullets.

"Corey Comparatore was a brave firefighter who died, [his] funeral [was] yesterday," Trump said. "Corey was a hero. And we will carry his memory in our hearts for all time."

Later in his speech, Trump conducted a "poll" with the audience members about who should become the Democratic nominee if President Biden steps down from the race.

"We're going to do a poll, and it's going to be a very nice poll and great. Who is your favorite candidate? Who would you like?" Trump said.

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Trump at rally

Former President and 2024 presidential nominee Donald Trump speaks during a campaign rally with Sen. and vice presidential nominee JD Vance at Van Andel Arena in Grand Rapids, Mich. (JIM WATSON/AFP via Getty Images)

"So who would you like to most run against, if you're us, if we want to win? Ready? Kamala Harris? Crooked Joe Biden?" Trump asked. The audience booed louder in response to Biden.

The former president also slammed Michigan Gov. Gretchen Whitmer, calling her a "terrible" leader.

"Well, you have a terrible governor here who did a terrible job. Whitmer – I'd like to run against her, actually," Trump laughed.

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Michigan is expected to be one of the most closely watched battleground states in November, and could narrowly determine who will serve the American people in the White House for the next four years.

Get the latest updates from the 2024 campaign trail, exclusive interviews and more at our Fox News Digital election hub.