Mehmet Oz and David McCormick, two of the top contenders in Pennsylvania’s crowded and divisive Republican Senate primary, took aim at each other over the issue of fracking as they faced off for the first time on the same stage.

The fireworks took place Wednesday morning at a candidates’ forum in Erie, Pennsylvania, organized and hosted by the Manufacturer & Business Association. Among the ground rules – the candidates were asked not to criticize each other.

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But roughly 10 minutes into the event, McCormick a former hedge fund executive, a West Point graduate, Gulf War combat veteran and Treasury Department official in former President George W. Bush's administration targeted Oz, the cardiac surgeon, author and well-known celebrity physician who until the launch of his Senate campaign late last year was host of TV’s popular "Dr. Oz Show."

Dr. Oz is running for U.S. Senate in Pennsylvania.

"On your shows, in your columns, you’ve argued for more regulation in fracking. You’ve made the case that there’s health effects from fracking. And you’ve argued for a moratorium in Pennsylvania like that’s in New York," McCormick charged.

A heated Oz, firing back, argued "that’s not true….that’s wrong. That’s a lie and you know it’s a lie."

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After the forum’s moderator intervened and chided McCormick for criticizing Oz, McCormick said "I think we should all be held accountable to our own words and what we’ve said."

Pennsylvania is one of the top states in the nation for hydraulic fracturing. The process, commonly known as "fracking," involves pumping a pressurized mixture of water, sand and chemicals underground into rock formations to dislodge oil and natural gas. 

Medical advice articles written in 2015 by Dr. Mike Roizen, then the chief medical officer at the Cleveland Clinic Wellness Institute, which also listed Oz as an author, warned of the potential health risks from the controversial technology to extract fossil fuels.

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Oz, as he runs for the Senate, has called for the "freedom to frack." And his campaign claims the views in the shared columns belonged entirely to Roizen, recently arguing that "Dr. Oz and Dr. Roizen have very different positions on energy policy and fracking."

McCormick (right) and Oz (left) are currently the top two GOP candidates in a recent Fox News poll for the race to succeed retiring Republican Sen. Pat Toomey.

Oz also spotlighted at the forum that he was endorsed this week by former longtime Texas Gov. Rick Perry, who served as Energy secretary during former President Trump's administration.

The verbal fistfight between Oz and McCormick is their latest confrontation over a host of issues, including China, charges that McCormick outsourced Pennsylvania jobs, and over Oz’s dual Turkish citizenship.

McCormick and Oz are currently the top two GOP candidates in a recent Fox News poll for the race to succeed retiring Republican Sen. Pat Toomey. It’s a crucial contest in a key general election battleground state and one of a handful of Senate elections across the country that could determine whether the GOP wins back the chamber’s majority in November’s midterms.

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McCormick and Oz were joined at the forum by Jeff Bartos, a real estate developer, philanthropist and 2018 Republican nominee for lieutenant governor, and veteran and conservative political commentator Kathy Barnette.

Barnette set off more fireworks late in the forum, when she interrupted Oz as he was delivering his closing comments.

Dr. Oz visits "Outnumbered Overtime with Harris Faulkner" at Fox News Channel Studios on March 9, 2020 in New York City. (Roy Rochlin/Getty Images)

As Oz emphasized, "We should all ask ourselves, why is everyone attacking me," Barnette interrupted, charging: "Because you’re a liberal."

After the forum’s moderator warned Barnette not to interrupt again, the candidate responded, "I have earned my place on this stage and I will not be told what I can and cannot say."

When Oz resumed his closing comments, he noted, "I don’t mind being attacked. I have pretty thick skin."

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Oz highlighted how he "decided that I would burn the boats and give up the television show, the top health show in the world" to run for the Senate.

"Imagine being so compelled, so worried about your country, that you’d give it all up and not feel an inkling of remorse for it," Oz said, "because now you can actually do what you know, at the end of your life, you'll look back on and realize was necessary, important, and perhaps the most important contribution you’ll make."

The Senate race in Pennsylvania is the most expensive in the nation, with over $50 million spent to run ads by the campaigns and outside groups backing the candidates. And the biggest spenders by far are Oz and McCormick, according to the latest data from AdImpact, a leading national ad tracking firm.

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Bartos, who once again repeated his charge that McCormick and Oz are "political tourists," emphasized that "they’ve come in and they’re spending tens of millions of dollars on television, and we’ve been on the roads, grassroots, for me five years, visiting all 67 counties multiple times."

Bartos also chided the verbal fisticuffs between McCormick and Oz, saying, "We can’t as conservatives spend our time fighting with each other."