Former Vice President Mike Pence argues that former President Donald Trump "and some of his imitators in the Republican primary" are walking away from core conservative values.

It's a charge the former vice president made in an interview with Fox News Digital on the eve of a highly-billed speech Pence will deliver on Wednesday titled "Populism vs. Conservatism: Republicans' Time for Choosing."

Pence will give his address at Saint Anselm College's New Hampshire Institute of Politics, a must-stop for White House hopefuls in the state that holds the first primary and second overall contest in the GOP presidential nominating calendar.

"I think we have a very clear choice that’s emerging, not just between candidates but between a philosophy of governance, and Republicans are facing a Republican time for choosing," Pence emphasized during his Fox News interview at a campaign stop in New Hampshire.

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Mike Pence speaks at Politics and Eggs

Former Vice President Mike Pence speaks at 'Politics and Eggs' at Saint Anselm College's New Hampshire Institute of Politics, on August 17, 2022 in Manchester N.H.  (Fox News )

"Time for choosing" is a clear nod to the late President Ronald Reagan, who famously used the line in a 1964 speech in support of conservative Barry Goldwater's presidential bid. That address has long been seen as a key moment in Reagan's transformation from Hollywood actor to politician, and eventually president and conservative icon.

Pence's speech in New Hampshire comes three weeks ahead of the second GOP presidential nomination debate, a Fox Business hosted showdown that will be held at the Ronald Reagan Presidential Library in Simi Valley, California

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"I really do believe that we’re in the midst of a healthy debate in the Republican Party today – whether or not we’re going to continue to hue towards that time honored conservative agenda of a strong national defense, American leadership in the world, limited government, fiscal responsibility, traditional values, and the right to life, or whether we’re going to follow the siren song of populism away from many of those same timeless conservative principles," Pence argued.

Pence said he aims to use his address "to frame that for people. I want people to know that I’m not only offering what I believe is a campaign that brings my experience and my record in the Congress and as governor and as Vice President to bare, but also I want people to see me as the most proven, consistent, conservative in this race and I’ll lead this party and I’ll this country back to those principles that have always made our country strong and free."

Former Vice President Mike Pence, a 2024 Republican presidential candidate, addresses the crowd at the Salem, New Hampshire GOP's annual Labor Day picnic, on Sept. 4, 2023 in Salem, N.H. (Fox News - Paul Steinhauser) (Fox News - Paul Steinhauser)

It's a message Pence first spotlighted during a speech at conservative Heritage Foundation last October in which he warned of the rise of populism in the GOP.

As he launched his 2024 White House campaign during a speech in June in Iowa, Pence highlighted the competing visions for the future of the Republican Party, and emphasized that the GOP must be the party of the Constitution.

The former vice president is currently polling in the single digits — along with most of the rest of the large field of contenders — in the latest GOP nomination polls, far behind his former running mate. Trump, who's making his third straight White House run, is the commanding front-runner right now in the Republican nomination race.

Pence, a former representative and Indiana governor whom Trump picked as his running mate seven years ago, highlighted that "when Donald Trump ran in 2016, he ran on a promise that we would governor as conservatives. And we did. For four years we rebuilt our military, we cut taxes, we rolled back regulations, unleashed American energy, and appointed conservatives to our courts at every level."

"But now, the former president and some of his imitators in the Republican primary make no such promise," Pence said, as he pointed to Trump and some of the other 2024 GOP presidential contenders.

Pence blasts Ramaswamy at first debate

Former Vice President Mike Pence and biotech entrepreneur Vivek Ramaswamy square off at the first Republican presidential nomination debate, on August 23, 2023 in Milwaukee, Wisconsin (Fox News)

One of his rivals Pence was likely referring to is Vivek Ramaswamy, a 38-year-old multimillionaire biotech entrepreneur and first-time candidate who's seen his standing in the polls rise as he runs as an outsider and leading Trump defender.

Since the two candidates repeatedly clashed at last month's first GOP presidential nomination debate, the 64-year-old Pence has taken aim at Ramaswamy's apparent fluidity on a number of issues, from his tax proposal to Russian's war on Ukraine, to the Sept. 11, 2001 terrorist attacks. 

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But top Pence campaign aides, speaking with reporters on the eve of the former vice president's address, emphasized that Wednesday's speech isn't about targeting any single candidate and is much broader in scope.

"Mike is trying to take a stand to remind our party of the value of conservatism," an aide said.

Former President Donald Trump

Former President of the United States Donald J. Trump delivers remarks at Windham High School in New Hampshire on August 8, 2023. (Erin Clark/The Boston Globe via Getty Images)

Trump, thanks to his dominance over the GOP the past eight years, has dramatically reshaped the party, fueling the base with working class support, and to a degree replacing conservative dogma with a more populist and nationalist agenda.

Trump Campaign Senior Advisor Jason Miller told Fox News that "President Trump’s victory in 2016 exposed the massive divide between voters around the Country and the Establishment Beltway Insiders who made terrible trade deals, allowed our Southern Border to become overrun, and never missed an opportunity to play World Cop. The conservative movement and the Republican Party have changed for the better, and nobody wants it to go back to the way it was before."

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But Pence campaign aides argued it's not too late to make the case for conservatism. 

And the former vice president, in his Fox News Digital interview, highlighted that "I believe that the majority of Republican primary voters, I believe the majority of Americans, know that the commitment to a strong national defense, American leadership, fiscal responsibility, and traditional values is an American agenda that will make our country more prosperous and more secure and more free."

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

Fox News' Rich Edson contributed to this report