Doug Mastriano has the fervent base. But Mehmet Oz is trying to reach Pennsylvania swing voters.

When Republican Senate candidate Mehmet Oz held a rally in Bucks County, he brought in Louisiana Sen. John Kennedy, a fairly traditional Republican who laces his political attacks with a Southern drawl and comic delivery.

When Doug Mastriano went to Bucks, the Republican nominee for governor invited Jack Posobiec, a bomb-throwing conspiracist who has targeted some prominent Jewish people with an antisemitic Twitter meme.

The two events in one of Pennsylvania’s most moderate swing counties reflect how the state’s top GOP candidates have diverged in their pitches to voters.

Mastriano has a devoted base of support who chanted his name at a September rally with former President Donald Trump. But even some fellow Republicans are cringing because he’s done little to expand his backing. Calling Mastriano an extremist, some have endorsed his Democratic rival, Attorney General Josh Shapiro.

Oz, at that same Trump rally, generated much less vocal enthusiasm. Republican voters still appear lukewarm toward him, according to polling. But unlike Mastriano, Oz is aiming for broader, if less excited, backing.

After clinging to Trump in the primary, the celebrity surgeon has tried to soften his profile and reach out to suburban swing voters and even some voters in deep-blue Philadelphia. Oz’s approach has Republicans talking up their hopes for “Shapiro-Oz” voters as a key to a Senate race that has shown signs of tightening.

Those hopes are a tacit admission that many Republicans are writing off Mastriano, and hoping Oz can outperform him in a nationally watched race that could determine control of the U.S. Senate.

“There are a lot of more moderate Republicans who are just not going to vote for Doug Mastriano but they’re OK with Oz,” said Jason High, who worked for former GOP gubernatorial nominee Scott Wagner.

It helps, of course, that, unlike Mastriano, Oz has run a more traditional campaign, with millions of dollars of national GOP money behind him, helping pound his Democratic opponent, John Fetterman, on TV. Mastriano, until this week, hadn’t run a single ad.

“Mehmet’s focus from the day after the primary was building a very broad-based general election coalition that could represent the whole commonwealth,” said Montgomery County Republican Jeff Bartos, an Oz primary rival who now chairs his Senate campaign.

(Bartos’ wife recently hosted a fund-raiser for Shapiro.)

While both Mastriano and Oz have deeply negative public images according to polling, Mastriano’s stances — on overturning election results, banning abortion entirely, and his ties to antisemitism — appear more likely to be viewed as disqualifying than simply disagreeable.

“The differentiation between Mastriano and Shapiro is so dramatic, and that’s why a lot of Republicans are going for Shapiro,” said Jim Greenwood, a former Republican congressman from Bucks County who is supporting the Democrat for governor.

Jane Galli, a retired math teacher and former Republican Radnor committeewoman, is one example.

”In all good conscience, I can’t vote for Mastriano,” said Galli, 71, pointing to his opposition to all abortions, without exceptions. But she attended a recent Oz event in Delaware County and plans to support him.

The Delaware County event was part of a string of recent Oz events in and around Philadelphia, and he was in Pittsburgh last weekend, targeting Democratic strongholds and the suburbs that surround them.

Recent polls, however, show Oz with roughly the same amount of support as Mastriano — suggesting his gains might mainly come not from swing voters, but from skeptical Republicans who have come around, and were always likely to support their party’s nominee eventually.

“A lot of what you’re seeing is Oz just bringing Republicans home” after a brutal GOP primary, High said.

Democrats say Oz’s hope for crossover votes is hamstrung by his deep-seated image problems, and what they say are equally unpopular policies beneath his general election pivot.

The celebrity surgeon’s favorability was about 20 percentage points underwater in a recent Marist poll, worse than Mastriano’s. And Democrats see abortion rights as an issue that will make Oz toxic to many swing voters. A recent Fetterman news release linked Oz and Mastriano, noting that both have described abortion as “murder.”

“If you needed any more evidence that Dr. Oz is one of the most radical anti-abortion candidates in the country, this is it,” Fetterman said in a statement.

Fetterman, meanwhile, on Tuesday launched a “Republicans for Fetterman” campaign highlighting GOP voters who support him.

“I want to elect someone who has the best interest at heart for everyone in Pennsylvania, not when it’s convenient in an election year,” Vince Tulio, a registered Republican from Montgomery County, said in a Fetterman news release.

But in a state where Democrats still outnumber Republicans, the GOP is more reliant on swing voters.

» READ MORE: After rallying with Trump, Mehmet Oz is pivoting toward the suburbs that have abandoned the GOP

Oz’s approach in some ways mirrors the GOP tactics in 2016, when Sen. Pat Toomey took a different approach than Trump and outperformed him in the Philadelphia suburbs, a key to the senator’s victory.

Oz has even used Toomey, the senator he’s running to replace, as a surrogate at events in Philadelphia and Pittsburgh. (Toomey isn’t seeking reelection.)

There’s at least one difference now at play: Toomey ran with the support of gun-safety groups that praised his support for broader background checks, a key selling point in the suburbs. Oz opposes that idea, and is now facing attacks from one of those same groups.

It’s an open question, though, how many swing voters still exist.

“Politics has become so tribal and so polarized and so much based on party ... that I’m not convinced there’s a lot of ticket-splitting that’s going to happen this time,” Greenwood said.

Other Republicans point to recent elections to argue that there are still enough to make a difference in a close race. In Chester County, for example, the GOP candidates for treasurer and auditor won more votes than Trump did in 2020, and triumphed statewide, while the former president lost.

“Are there a ton of Shapiro-Oz voters walking around out there? And the answer is no,” said Muhlenberg College pollster Chris Borick. “Is there a segment that could be important in a tight race? And the answer is probably yes.”

His polling found weaknesses for Fetterman with older suburban voters who favor Shapiro.

“A lot of it is the product of Oz’s focus over this fall and his spending on making Fetterman look soft on crime, too radical for Pennsylvania on a bunch of social issues,” Borick said, pointing to legalizing marijuana, a top Fetterman priority, as one stance that is less appealing to older voters.

“Then you get to Fetterman’s brand: really attractive to some voters, younger, working class,” Borick said. But “for a more buttoned-down, older audience, [it] isn’t a natural fit.”

Since winning the GOP primary Oz has tried to shave the edges off some of his key positions.

After emphasizing his antiabortion credentials during the primary, telling some supporters the procedure amounts to “murder,” he has since said he doesn’t believe in prosecuting doctors who perform abortions. He has sidestepped questions about a proposed national ban after 15 weeks of pregnancy.

And after nodding to Trump’s baseless claims about the 2020 election — saying “we cannot move on” — Oz recently said he would have certified Pennsylvania’s vote if he had been in the Senate. His campaign refused to answer that question when The Inquirer asked during the primary.

» READ MORE: Mehmet Oz called abortion ‘murder’ during the Pa. Republican Senate primary, recording shows

Democrats chalk up Oz’s gains on Fetterman to a money-bomb from Senate Minority Leader Mitch McConnell (R. Ky.), whose affiliated super PAC has been bombarding television with attacks on Fetterman, including $18 million since the May primary, according to AdImpact, which tracks political advertising.

The governor’s race appears to be trending more strongly Democratic because Fetterman is lagging Shapiro, who has had the benefit of facing few attack ads.

The gap on the Democratic side suggests there might still be a sizable swath of Democratic votes available to Fetterman.

But so far he hasn’t closed the deal with some voters willing to support his party. That might leave a door open for Oz — even if the governor’s race turns into a rout.

Staff writer Julia Terruso contributed to this article.