Mehmet Oz bounded into a suburban Philadelphia banquet hall, arms raised like Rocky as the crowd rose to its feet.

“Do we want a dose of reality today?” asked the celebrity surgeon known as “Dr. Oz.” It could have easily been a studio audience that shouted back: “Yeah!”

“All right, let’s have a seat and let’s talk about this stuff!”

The veteran showman is used to driving public conversations. After making his name on daytime TV, Oz’s public profile and wealth helped power America’s most famous cardiothoracic surgeon to an early lead in Pennsylvania’s crucial Republican Senate primary — much like another rich celebrity who splashed into GOP politics not that long ago.

But now his top Republican rival has turned Pennsylvania’s airwaves against Oz, hitting him with a gold-plated political sledgehammer. Former hedge fund executive David McCormick and his wealthy allies have mined Oz’s very public past to question his conservative credentials and paint him as a Hollywood elitist.

A nearly $8 million advertising barrage — including almost $6 million in February — has blasted Oz on issues including gun laws and abortion. And it has had an impact, driving up negative perceptions of the TV star and, according to public polling, vaulting McCormick into the lead after Oz started as the clear front-runner.

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Oz is answering with a blitz of public events, supplementing his own heavy TV spending with in-person performances aimed at addressing skeptics head-on, with a splash of star power. In those showcases, Oz argues that after years of fighting the conventional wisdom on medicine and science (though with sometimes misleading medical advice), he’s got the thick skin to absorb flak from powerful critics.

“I’m not trying to be aggressive or abrasive. I’m not purposely picking fights, but I’m a porcupine. And I will assertively say what I think has to be said,” Oz, in a charcoal suit and open shirt, told the crowd last week in West Chester. “I did not decide to campaign for office because I thought it would be a fun joyride.”

The attacks are no joyride.

Oz — who says he put $10 million of his own money into the campaign — has purchased $8.4 million of airtime through Saturday, the most of any Senate candidate in the country, according to AdImpact, which tracks political advertising. But McCormick and his allies have outpaced him.

McCormick’s campaign spent almost $6.4 million on ads running through this week, despite joining the race more than a month later. And the super PAC supporting him, Honor Pennsylvania, has dumped $7.7 million of attack ads on TV, the most any entity has spent so far on a single Senate race, part of a $12 million plan. A pro-Oz super PAC has spent just $1.2 million.

All told, McCormick and his allies have outspent Oz and his friends on TV by almost 50%.

» READ MORE: The Pennsylvania Senate money race in 8 charts

The result: A Fox News poll released Tuesday found McCormick with support from 24% of Pennsylvania Republican primary voters, compared with 15% for Oz. No other candidates topped 9%. It’s a stark reversal from just a couple of months ago and mirrors what GOP insiders say they’ve seen in private surveys.

“As Dave McCormick’s momentum continues to grow, Mehmet Oz is being rejected by Pennsylvania conservatives because they see through the fraud of his candidacy,” said McCormick spokesperson Jess Szymanski.

McCormick’s team nearly fell over themselves in glee when Oz was pictured last month on his hands and knees kissing his newly christened star on a red carpet on the Hollywood Walk of Fame. The photo features in a recent super PAC attack ad calling Oz a “Hollywood liberal.”

“Oz has 2,000 hours’ worth of television that belies the message he’s trying to advance,” said Jim Schultz, a McCormick adviser.

Oz’s campaign points to crowds coming to see him by the hundreds, including stops Tuesday in Blue Bell and Glen Mills and last week in northwestern Pennsylvania, Hershey, and West Chester. The campaign argues that as people see Oz in person, he’s winning them over.

“Not every person who attends a Dr. Oz event walks in the door voting for him, but the vast majority leave being all in,” said Oz spokesperson Brittany Yanick.

One positive glimmer for Oz in the Fox poll: His supporters were much more firmly committed to him than McCormick’s. The poll also found a large number of undecided voters, leaving room for the race to shift.

McCormick and Oz are the two leading Republicans in the race to replace Sen. Pat Toomey, a Republican who isn’t seeking reelection. The race is among the most crucial in the country, one of a handful likely to decide which party controls the Senate. And it’s already by far the most expensive.

Oz in many ways channels former President Donald Trump, but with a softer touch. Despite his wealth, success, and a TV career launched by Oprah, he casts himself as someone who’s fought the establishment — whether that’s government, the media, or the medical community.

“Whenever the New York Times writes a negative article about me it’s a badge of honor,” he said in West Chester, where the playlist included a Trump staple: Lee Greenwood’s “Proud to be an American.”

He says he’d focus in Washington on healthcare, education — particularly school choice — and foreign policy.

The real fight is likely still looming, as the May 17 primary draws closer. Republicans are wondering how much Oz will spend to hit back — and question if he can keep pace with McCormick, who until recently led the world’s largest hedge fund, is married to a Goldman Sachs executive, and whose rich friends are pouring in millions to slam Oz.

» READ MORE: David McCormick’s longtime praise for China and trade could bite his Pa. Senate run

McCormick has his own vulnerabilities, most notably his former hedge fund’s investments in China, and the race is still in its early stages. But several Republicans warned that Oz’s responses may lose their punch if McCormick’s team destroys his credibility first.

If Oz and McCormick punch each other out, it could also open a door for other candidates — like Carla Sands, Jeff Bartos, or Kathy Barnette. But none of them can compete financially.

Before each of his public events, Oz’s team blasts text messages and phone calls to Republican voters in the area, rounding up hundreds to come see him pull a few people from the crowd, check their blood pressure, and take questions.

Several at the West Chester event, including some who had clearly seen the attack ads, said he disarmed their skepticism.

“I wanted to see if he was really a RINO,” said Anne Emerson, 58, of West Chester, referring to the phrase “Republican in Name Only,” as he’s been dubbed by McCormick’s super PAC. “I thought he did a good job. He seemed real, he seemed sincere.”

Emerson wants to elect a “true America First conservative.” She said Oz “reminded me of Trump.”

“Family values, he doesn’t come from politics,” she said. “He has no skin in the game.”

That’s a parallel Oz is eager to draw, frequently describing himself as an “outsider.” He talks up his friendship with Trump, while his campaign compares McCormick to former Florida Gov. Jeb Bush: the 2016 insider choice who flopped with GOP voters.

Even some Republicans who don’t support Oz described being impressed by his attentiveness and willingness to face questions in private meetings.

“He’s a very gregarious guy, he’s an entertainer,” said Rob Gleason, a former state GOP chairman who supports McCormick. But he added that Oz’s positions put him out of step with Republican primary voters.

For example, Oz has in the past been open to “red flag laws,” which allow judges to remove guns from people whose family members or friends believe they pose a risk to themselves or others. It’s an idea Trump embraced in 2019.

Asked this month about the Second Amendment, Oz told conservative radio host Chris Stigall about owning “a dozen guns” and said, “We cannot compromise our ability to protect ourselves.”

» READ MORE: Mehmet Oz says he’s a Pennsylvania resident now. So why’s he still hanging out in his New Jersey mansion?

Oz has long said he is personally against abortion but raised concerns as recently as 2019 about laws that would severely restrict the procedure early in pregnancy, and said he wouldn’t want to impose his views on others. He now describes himself as “strongly pro-life” and told Stigall, “I believe life starts at conception.” He had danced around the question of when life begins when pressed by Fox News in December.

He didn’t get into such specifics in West Chester, instead telling the audience about operating on a five-day-old heart: “When you see the majesty of that little muscle in there ... you can’t fathom the idea of snuffing that out.”

Anita Edgarian wasn’t totally sold. The 57-year-old from West Chester said that as an Armenian American, she wanted to hear more about Oz’s dual Turkish citizenship, another issue his rivals have pressed.

“I mean you look at him today, he’s flawless. He says all the right things in the right environment,” she said, gesturing to the polished set and sound system. “But we have to be careful who we are electing. I want to know more.”