GREENSBURG, Pa. — Former President Donald Trump aimed to flex his muscles as a GOP kingmaker here Friday night, praising Senate candidate Mehmet Oz while hammering his chief primary rival, David McCormick, as a weak Republican who would fit in with Trump’s perceived nemeses.

“Dr. Oz is running against the liberal Wall Street Republican named David McCormick,” Trump said in a rally at a soggy, rainy fairground in Southwestern Pennsylvania. Referring to his “Make America Great Again” slogan, Trump added: “He may be a nice guy, but he’s not MAGA.”

Trump likened McCormick to “Washington establishment” Republicans he has clashed with including Senate Minority Leader Mitch McConnell, Rep. Liz Cheney, and Sen. Pat Toomey, who voted to convict Trump at his second impeachment trial.

The attacks, and praise for Oz, came as Trump hoped to help push the celebrity surgeon to victory in a close and contentious GOP primary. Trump’s words will likely be potent fodder — replayed often — as a close Senate race heads into its final days.

Oz and McCormick, a former hedge fund CEO who served in the George W. Bush administration, are leading primary polls in one of the country’s most critical Senate races, with conservative commentator Kathy Barnette not far behind them. A large swath of GOP voters are still undecided just 10 days before the May 17 primary.

Having just helped decide the Republican Senate winner in Ohio, Trump aimed Friday to replicate the feat after endorsing Oz last month — though he didn’t make an endorsement in Pennsylvania’s crowded Republican primary for governor, despite speculation that he might.

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After about an hour focused on other topics, Trump vouched for Oz’s conservative credentials in the face of millions of dollars of attack ads and criticism from his GOP rivals. But he just as sharply hammered McCormick, who had relentlessly sought Trump’s endorsement and spent millions presenting himself as an “America First” Republican.

Trump, speaking to several thousand supporters set up on a muddy field and wearing ponchos, fixated on McCormick’s past criticisms of him after the Jan. 6 Capitol riot, predicting McCormick would “fold” in the Senate. By contrast, Trump said Oz “has the best chance to win” and “will fight to the end, and he will always have your back. We can always count on Dr. Oz.”

At another point, referring to Oz’s TV career, Trump said: “He’s on that screen, he’s in the bedrooms of all those women, telling them good and bad, and they love him.”

Deep into a winding speech, and with much of the crowd wet and cold, the responses were relatively muted compared with most Trump rallies.

Trump’s decision to weigh in on key Republican races has shaped up as a test of his lasting influence on the GOP. He scored a major victory earlier this week when author J.D. Vance surged to victory in Ohio’s Republican Senate primary on the heels of a Trump endorsement.

He’s hoping to replicate that success with Oz in Pennsylvania, home to a nationally watched race that could decide control of the Senate. Toomey isn’t seeking reelection.

Oz, who has faced sharp questions about shifting positions on core conservative issues like abortion and gun rights, spoke to a still sparse crowd under the rain, saying he believes life begins at conception, opposes restrictions on guns, and that he’d gone “to war” with big pharmaceutical and technology companies.

“The establishment, they hate us because we threaten the status quo. We go after that,” Oz said. “We don’t want a Wall Street-Washington revolving door.”

And he touted Trump’s endorsement. “He wrote that announcement himself, because I am smart, because I’m tough as nails, and I will never let you down,” Oz said.

» READ MORE: Get to know the 2022 candidates for Pa. Senate and governor

McCormick and his allies have spent millions driving up negative perceptions of Oz. And before the rally, there was deep skepticism among some in the crowd.

“People in Pennsylvania overwhelmingly don’t want Oz,” said Debby Lee, 55, who drove five hours from Olyphant, just outside Scranton, to see Trump.

“He’s pro-red flag laws,” she said of Oz, referring to laws that allow courts to temporarily take firearms from individuals believed to be a danger to themselves or others. “He’s anti-Second Amendment. He’s pro-abortion.”

Lee said Trump probably endorsed Oz because he thought the doctor had the best chance of winning in November, but she prefers Barnette.

When U.S. Rep. Guy Reschenthaler (R., Pa.) took the stage and began explaining why he was an early Oz supporter, some in the crowd booed.

Fayette City resident Ryan Shaw, 43, said he came to see Trump, but he’s not sold on Oz.

”I just don’t trust him. He’s friends with Oprah and all these liberals,” said Shaw, who works in construction. “He’s Hollywood.”

But Shaw said he doesn’t trust any of Oz’s Republican primary rivals either, and he would hear Trump out on Oz.

Lorraine Porch was planning to vote for Oz even before Trump made his endorsement.

”I like Oz, I do,” said Porch, 77, who lives near Pittsburgh. As for Oz’s past statements on abortion and other issues, ”I don’t think he feels that way anymore. It’s in the past. People have the right to change their minds.”

Polls suggest that Oz enjoyed some bump from Trump’s endorsement, but not enough to seal the race.

Hours before the event, McCormick rolled out one of his top surrogates, former Trump Secretary of State Mike Pompeo, to hammer Oz over his dual citizenship with Turkey. It’s a theme that the McCormick campaign has aggressively pressed in the race’s final days — but that even some other Republican candidates have criticized as xenophobic.

Pompeo noted that Oz voted in Turkey’s 2018 election, and has an endorsement deal with Turkish Airlines, which is mostly owned by the Turkish government. He said Oz should explain “the scope and depth of his relationship with the Turkish government.”

McCormick allies have run ads warning ominously that Oz would “betray us.”

Oz, who was born in the United States to immigrant parents, has said he maintains dual citizenship to care for his ailing mother, who lives in Turkey. He has also said he would renounce his Turkish citizenship if elected to the Senate.

“These are pathetic and xenophobic attacks on Dr. Oz by David McCormick, who should be ashamed of himself,” Oz spokesperson Brittany Yanick said. “Now that he lost President Trump’s endorsement, he’s resorted to sad and desperate attacks that are no different than the tropes used against Catholics and Jews.”