DURHAM, N.H. - Democratic Gov. Gretchen Whitmer of Michigan says that Republican vice presidential nominee Sen. JD Vance of Ohio is a changed man.

Former President Trump, the GOP presidential nominee, and his campaign are confident that thanks to Vance's blue collar roots, the senator will help the Republican ticket in the crucial battleground states of Pennsylvania, Michigan and Wisconsin, which have long been part of the Democrats' blue wall.

Asked by Fox News if she agreed with the Trump campaign's argument regarding Vance, Whitmer answered "if it was the JD Vance who wrote Hillbilly Elegy maybe. But it’s a very different person. It’s a person who has absolutely betrayed those values and that book and has become something that is just a reflection of Donald Trump."

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JD Vance speaks during the Republican National Convention

Senator JD Vance of Ohio, the GOP vice-presidential nominee, delivers his acceptance speech during the Republican National Convention at the Fiserv Forum in Milwaukee, Wisconsin, on Wednesday, July 17, 2024.  (Al Drago/Bloomberg via Getty Images)

"Maybe even more concerning than a reflection of Donald Trump," Whitmer added. " I would say that that kind of leadership is not something that's going to resonate and that's why we've got to make sure people know who he is."

Asked for a response, Vance in a statement to Fox News argued that "career politicians like Gretchen Whitmer can lie about me all they want, but I’m still always going to put American workers and families first and foremost because I’ll never forget where I came from."

"It’s career politicians like her who support the radical Kamala-Biden agenda to leave our southern border wide open, strangle American energy, kill the automobile industry with their electric vehicle mandates, and drive up the cost of living through inflationary spending who clearly have forgotten about the people she’s supposed to be representing," Vance charged.

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Vance grabbed national attention a couple of years ago after writing "Hillbilly Elegy," which tells his story of growing up in a struggling steel mill city in southwest Ohio and his roots in Appalachian Kentucky. It became a New York Times bestseller and was made into a Netflix film. The story spotlighted the values of many working-class Americans who became supporters of Trump's policies.

Vance's working-class parents divorced when he was young, and his mother struggled for years with drug and alcohol abuse. Vance was raised in part by his maternal grandparents.

After high school graduation, Vance enlisted in the U.S. Marine Corps and served in the Iraq War. He later graduated from Ohio State University, earned a law degree at Yale University, and later moved to San Francisco and worked as a principal in a venture capital firm before heading back home to Ohio where he ran for the Senate in 2022.

Donald Trump applauds as Republican vice presidential nominee J.D. Vance gestures on Day 2 of the Republican National Convention

Republican presidential nominee and former President Donald Trump applauds as Republican vice presidential nominee Sen. J.D. Vance gestures on Day 2 of the Republican National Convention, at the Fiserv Forum in Milwaukee, Wisconsin, on July 16, 2024.  (REUTERS/Elizabeth Frantz)

Vance was a vocal critic of Trump when the former president first ran for the White House in the 2016 cycle. 

However, Vance eventually supported Trump, praising the former president's tenure in the White House, and in a Fox News interview in 2021, he apologized for his earlier criticism of Trump.

Trump's endorsement of Vance days before the 2022 GOP Senate primary boosted him to victory in a crowded, competitive and combustible nomination race. After winning election to the Senate, Vance quickly became a top supporter in the chamber of Trump's America First agenda and a champion of the former president's MAGA movement.

Gretchen Whitmer argues that JD Vance has 'absolutely betrayed' his blue collar roots

Michigan Gov. Gretchen Whitmer campaigns on behalf of presumptive Democratic presidential nominee Vice President Kamala Harris, at a house party in Durham, New Hampshire on July 25, 2024 (Fox News - Paul Steinhauser)

Whitmer, a two-term governor of a crucial midwestern battleground state and a leading figure in the Democratic Party, spoke with Fox News at a house party in Durham, New Hampshire. It was her third and final campaign stop on Thursday in the key New England swing state on behalf of Vice President Kamala Harris, who this week replaced President Biden as the party's presumptive presidential nominee.

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President Biden, in a blockbuster announcement Sunday, ended his 2024 re-election rematch with Trump and endorsed his vice president. Biden made his move amid mounting pressure from within the Democratic Party for him to drop out after a disastrous performance in last month's first presidential debate with Trump.

The embattled president's immediate backing of Harris ignited a surge of endorsements of Harris by Democratic governors, senators, House members and other party leaders. By Monday night, the vice president announced that she had locked up her party's nomination by landing the backing of a majority of the nearly 4,000 delegates to next month's Democratic National Convention. She has also hauled in a staggering $129 million since Biden's announcement, her campaign touted on Thursday morning.

Gretchen Whitmer makes three stops in New Hampshire on behalf of Kamala Harris

Michigan Gov. Gretchen Whitmer joins Democratic activists at a house party in Durham, New Hampshire for Vice President Kamala Harris, on July 25, 2024 (Fox News - Paul Steinhauser)

"I was grateful and honored to be a co-chair of the Biden campaign. I am similarly grateful and honored to be a co-chair of the Harris campaign," Whitmer said to cheers from the couple of hundred people at the house party.

No Republican has carried New Hampshire in a presidential election in 24 years, but recent polling suggested a margin-of-error contest between Biden and Trump

But two new public opinion surveys in the state released on Thursday indicated Harris holding single-digit leads over Trump.

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