HARRISBURG — Democratic U.S. Sen. Bob Casey of Pennsylvania and Republican challenger Lou Barletta jousted Monday over the Trump administration’s tax-cutting bill as Barletta criticized the federal investigation into Russian interference in the 2016 election won by President Donald Trump as going down “rabbit holes.”

Barletta, a four-term congressman from northeastern Pennsylvania and staunch Trump supporter, appeared in Philadelphia with Vice President Mike Pence, who flew in to promote Trump’s tax bill and to headline a fundraiser for Barletta.

Asked by reporters about fresh criticism by Trump of special counsel Robert Mueller’s investigation into Russian election interference, Barletta said the investigation has run far afield of whether Trump’s campaign colluded with Russians.

“And now we’re talking about porn stars and relationships,” Barletta said. “I don’t know how many different rabbit holes we’re going to go down. But ... investigating relationships with porn stars from colluding with the Russians in elections are pretty far apart.”

Mueller’s probe is separate from the FBI investigation into payments to porn actress Stormy Daniels from Trump’s longtime lawyer before the election to keep quiet about a sexual relationship she says she had with Trump.

Asked whether he agrees with Trump’s characterization of Mueller’s probe as a “witch hunt,” Barletta said, “call it what you want.”

But, he said, there’s been no sign of collusion and “now we’re talking about relationships with a porn star. Do you think that’s fair?”

Speaking to the Pennsylvania Press Club in Harrisburg, Casey attacked the Trump administration’s tax-cutting bill, saying the vast majority of benefits are flowing to the nation’s highest earners.

Afterward, Casey said the bill “gave away the store to the top 1 percent” and could have been written to deliver a far bigger tax break to the middle class.

“There are some folks in the middle that will get a tax break, but it’s a lot smaller of course than even in a proportional sense than what the top 1 percent will get,” Casey said.

Barletta said the tax cuts are boosting the economy and the vast majority of people are benefiting, even if companies are using cash from tax cuts to buy back shares.

Barletta introduced Pence at a Philadelphia hotel in the latest event promoting the administration’s tax-cutting law organized by America First Policies, a nonprofit that promotes Trump’s agenda. Barletta badly lagged Casey in fundraising as of July 1, and no independent poll puts Barletta within striking distance of Casey.