Need proof that the political network funded by billionaire Charles Koch is breaking up with some Republicans, just when its plentiful campaign contributions could help score victories in November's midterm elections?

Consider U.S. Rep. Lou Barletta's lagging challenge to U.S. Sen. Bob Casey, compared with former State Sen. Scott Wagner's challenge to Gov. Wolf's bid for reelection.

Both Republicans, Barletta from Hazleton and Wagner from York, won enthusiastic endorsements from President Trump during an Aug. 2 rally in Wilkes-Barre.

That came less than a week after the donor network founded by Koch and his brother, David, met in Colorado Springs and publicly distanced itself from Trump. Barletta was one Republican singled out for criticism there, according to the Washington Post.

To the Koch network, Trump has become too "divisive."

In response, the president tweeted, "The globalist Koch Brothers, who have become a total joke in Republican circles, are against Strong Borders and Powerful Trade."

Barletta's Senate race could present an opportunity for Americans for Prosperity, started in 2004 with funding from the Koch brothers, whose private, Kansas-based conglomerate has businesses with interests ranging from manufacturing to energy to finance.

A Morning Consult tracking poll for the midterm elections found in July that just a third of Pennsylvania's voters think Casey, a Scranton Democrat, deserves reelection, while 43 percent approve of the job he is doing in the Senate and 32 percent disapprove.

Still, an average of polls in the race, compiled by the website Real Clear Politics shows Casey with a 16-point lead, mostly because the challenger is unknown in many parts of the state.

That gives Barletta a real shot in shifting the narrative, if he has the resources to tell his story or some benefactor who can help from outside.

That's exactly the sort of help the AFP is known for.

Wagner faces the same rough road as Barletta. The Real Clear Politics polling average shows he too trails by 16 points in his bid to unseat Wolf, a Democrat from Mount Wolf.

AFP announced last week that it would oppose Wolf on Wagner's behalf, a potentially substantial boost in outside funding in the race.

And Barletta? AFP launched a campaign on May 24, nine days after Barletta easily won the Republican nomination for the Senate race, to "hold accountable" the four-term congressman for his support of a $1.3 trillion omnibus budget package in March.

That included a mailer that said: "Barletta voted to increase waste that helped push spending to more than $4 trillion this year alone."

Larry Sabato, director of the University of Virginia's Center for Politics, said that March budget vote was "exactly what AFP has stood against for many, many years." So the group took action, he said.

"They've decided to move away from too close an association with the Republican Party," Sabato said. "When the AFP takes a stand, I've learned, they stick with it. Come what may. They face the consequences. They're tough."

AFP has demonstrated electoral power before in Pennsylvania. The group supported U.S. Sen. Pat Toomey, a Lehigh County Republican who narrowly won a second term in 2016 over Katie McGinty, a Democrat from Wayne.

AFP poured nearly $2.6 million into independent expenditures to oppose McGinty, according to Federal Election Commission records.

Beth Ann Mumford, AFP's state director in Pennsylvania, said the group hasn't "made any announcement on the Senate race," though she did tout its support for Wagner.

"We have also spent the summer making tens of thousands of calls and door knocks urging folks to call Sen. Casey and ask him to support Judge Kavanaugh's confirmation to the U.S. Supreme Court and work to make tax reform permanent," Mumford added in an email.

Barletta could certainly use AFP's help. Campaign finance reports filed in mid-July showed he had $1.6 million in the bank, compared with Casey's $9.8 million.

Sabato, who prognosticates political races on a website he calls Sabato's Crystal Ball, said Republicans in Washington who follow Senate races see Casey in a strong position to hold off Barletta. That could be another factor in AFP staying on the sidelines in the race.

Barletta has tried to make the best of AFP's criticism, using it to paint himself as more of a centrist than Casey.

"I'm being attacked from the right by the Koch brothers and I'm being attacked by the far left by Bob Casey," Barletta told the Pennsylvania Press Club in Harrisburg on June 25. "So I must be perfect for Pennsylvania."