Republican gubernatorial candidate, Ed Gillespie, right, listens as Corey Stewart, left, gestures during a debate at Liberty University in Lynchburg, Va., Thursday, April 13, 2017. (AP Photo/Steve Helber)’

Virginia gubernatorial candidate Ed Gillespie’s Republican rivals on Thursday tried to cast the GOP front-runner as a Washington insider and member of the party establishment as Mr. Gillespie, Corey Stewart, and Frank Wagner squared off at a GOP debate held at Liberty University in Lynchburg, Va.

Mr. Stewart, chairman of the Prince William County Board of Supervisors, referred to Mr. Gillespie as a “30-year lobbyist from Washington, D.C.” and called his tax plan a “charade,” saying it relies on unspecified revenues that can’t be counted on to come to fruition.

“And just like the person who endorsed him, our former Governor [Bob] McDonnell, and he said he was going to decrease taxes, but we know what the establishment does,” Mr. Stewart said. “They simply go in there and then they say well, sorry, we can’t do it, and they’re going to increase taxes.”

Mr. Wagner, meanwhile, referred to a description of Mr. Gillespie, a former Republican National Committee chairman and adviser to President George W. Bush, as a “24-carat, gold-plated Washington insider.”

Asked directly by Mr. Stewart to identify a specific spending cut in his tax plan, Mr. Gillespie held his fire, saying the night was still young.

He generally refrained from responding directly to the personal potshots and instead spent his time talking up his own plans. 

“The answer is not to increase taxes on hardworking Virginians - the answer is to cut our taxes, get more Virginians back to work in high-paying jobs, and that will result in more revenue to our treasury in Richmond,” Mr. Gillespie said.

Mr. Gillespie has been leading in recent polling on the GOP primary candidates. He had 28 percent support to Mr. Stewart’s 12 percent and Mr. Wagner’s 7 percent in a Quinnipiac poll released this week, though more than half of Republican voters said they were still undecided.

Mr. Gillespie lost to Sen. Mark R. Warner in a close U.S. Senate race in Virginia in 2014.

Mr. Stewart served as President Trump’s Virginia state chairman but was fired in October after participating in a protest outside Republican National Committee headquarters.

He also ran unsuccessfully for the GOP nomination for lieutenant governor in 2013 and is closely associated with his county’s tough policies toward illegal immigrants.

Mr. Wagner, a state senator who represents parts of Virginia Beach, has served in the state legislature as a senator and as a member of the House of Delegates for more than 25 years.

Mr. Gillespie, Mr. Stewart, and Mr. Wagner are looking to hand the GOP its first win in a major statewide election since 2009, when Republicans swept the governor, lieutenant governor, and attorney general races.

Current Gov. Terry McAuliffe, a Democrat, is prohibited from seeking a second consecutive term.

In 2013, Mr. McAuliffe helped break a decades-long streak of Virginia voters picking a governor belonging to the opposite party of the incumbent U.S. president.

Mr. McAuliffe is supporting Lt. Gov. Ralph Northam in the race. Mr. Northam is battling former Rep. Tom Perriello to be the Democratic nominee.