Weeks after receiving Trump's endorsement, Pennsylvania Rep. Meuser opts against challenging Shapiro: Sources

At a rally in Pittsburgh in May, Pennsylvania Republican Rep. Dan Meuser received the most powerful co-sign in Republican politics: an endorsement from President Donald Trump in the upcoming gubernatorial race.

"He's been a great congressman," Trump said of Meuser, one of his top allies in the state. "And if you run, you have my full support. And you'll win. The people are going to get it real fast."

But after months of speculation, Meuser has recently told associates he will not enter the race to challenge Pennsylvania Gov. Josh Shapiro, three people with knowledge of his conversations told ABC News.

He delivered the news to Trump on Saturday over the phone, someone familiar with the call told ABC News. A White House spokesperson declined to comment.

The decision from Meuser, who declined to comment for this article, reflects the challenging environment Republicans could face in the upcoming midterms in competitive states such as Pennsylvania and against popular Democrats such as Shapiro.

"The fact is, Josh Shapiro is going to be reelected governor of Pennsylvania. It's not a question of if, it's a question of [by] how much," predicted Larry Ceisler, a Philadelphia-based public affairs executive and a Democrat.

Shapiro "has and will have a very large campaign war chest," added Ceisler, venturing that Meuser "doesn't feel like being a sacrificial lamb."

Christopher Nicholas, a Republican political consultant in Pennsylvania, told ABC News that Shapiro "has made a lot of friends nationally that he can use for fundraising, and he's made a lot of enemies nationally, which a Republican can use for fundraising."

Other Republicans are in the mix for the race at the top of the ticket, which could reverberate down the ballot: A strong Republican performance could help boost Republicans in vulnerable House districts -- which, in turn, could determine control of Congress in 2026.

Treasurer Stacy Garrity is seriously considering a run, according to someone close to her, and some Republicans in the state believe she would earn the backing of the state party if she entered the race.

In a statement, Garrity told ABC News, "Congressman Meuser is my representative, and I truly value the strong relationship we've built over the years. I commend him for his principled leadership in Congress and devotion to the people of the 9th District.

"I will have an announcement about the future of my career in service very soon," she added.

Also weighing a bid is state senator Doug Mastriano, the Republican nominee for governor in 2022 whose election denialism and anti-abortion stances doomed his bid, which ended in a 15-point defeat to Shapiro that fall.

Mastriano has floated a campaign in public radio interviews in recent weeks.

A representative for Mastriano did not return a request for comment.