Fight between Rothfus, Lamb for 17th District

businesses at a competitive disadvantage.

Mr. Rothfus also distanced himself from the several Republicans who said Mr. Lamb won in the bright red 18th only because he ran as a conservative, asserting that a Republican “wouldn’t want to raise taxes on small businesses.”

Mr. Lamb, a 33-year-old former federal prosecutor, did run his last campaign as more of a moderate. He “walked the middle path” by saying he wouldn’t vote for Nancy Pelosi as House Democratic leader, among other things, said Franklin & Marshall political analyst G. Terry Madonna.

This time, Mr. Lamb’s message is similarly that of a pragmatist.

“My message to voters is again that I’m here to work for you. I’m not here because of the national party leadership of either party,” Mr. Lamb said. “I’m here to do things like focus on jobs and infrastructure and taking on the heroin epidemic and fighting to preserve Social Security and Medicare. Those are the important things for Western Pennsylvanians no matter what political party you’re in.”

The influence of Donald Trump on the race, as in many others across the country, could be outsize. Unlike Mr. Rothfus’s district that was carried by Mr. Trump by more than 20 points, the new 17th went to him by about 2 percent.

Mr. Rothfus’s views are in line with the president’s, Mr. Madonna said. Democrats take that a step further.

“I think people look at that and are concerned that that’s going to make him a lot less willing to compromise on things and actually get stuff done,” Democratic activist and consultant Ray Linsenmayer said, adding that Mr. Rothfus is “ideologically tied” to the president.

Mr. DeMarco, the state Republican committeeman, said Mr. Rothfus “isn’t a rubber-stamp” for anyone, but has a relationship with the White House that allows him to better advocate for help in the region.

The race for the 17th is considered a “toss up” by the Cook Political Report, though Mr. Wasserman called that rating generous to Mr. Rothfus “because Lamb couldn’t have asked for a better district in which to run for a full term.”