The political battle over Pennsylvania’s next legislative maps is intensifying, with Republicans attacking one of the proposed maps and the integrity of the chair of the commission that drew it.

At issue is the state House map proposed last week by the five-member Legislative Reapportionment Commission. That map favors Republicans, but significantly less so than the current one, according to a detailed data analysis conducted for The Inquirer by the nonpartisan Princeton Gerrymandering Project.

The House Republican leader, who sat on the commission, said Tuesday that his input had been largely ignored. He also questioned whether the commission chair had a pro-Democratic agenda. Another key Republican lawmaker said the map violates the state constitution.

“This map needs to go,” Rep. Seth Grove (R., York) said at a news conference Tuesday. “They need to redo the entire thing to make sure we do not have unconstitutional districts done for partisan gerrymandering.”

And other GOP lawmakers also took aim at the chair, Mark Nordenberg.

Nordenberg, appointed to lead the five-person commission by the Democratic-controlled state Supreme Court, is the former longtime chancellor of the University of Pittsburgh and the current chair of its Institute of Politics.

He defended the maps and the redistricting process in an interview Tuesday, denying any partisan bias and saying district boundaries were drawn with input from both parties and designed to be fair and lawful.

“Every caucus had the opportunity to fairly participate in the process, so it’s certainly not my map, and it’s not the map of the Democratic caucus,” he said. “If I were to draw the map on my own, I’m sure I would do things differently. … This is what emerged from a process that engaged all of the interested parties.”

But Republicans, enraged by a map that could erode their long-held majority, are taking aim directly at Nordenberg.

» READ MORE: Is the new Pa. House map better for Democrats or Republicans? We tested it.

The new maps, which are drawn every 10 years to reflect population changes across the state, will shape political power for the next decade. Democratic Gov. Tom Wolf has long wielded his veto pen to block GOP legislation, but with the prospect that a Republican could succeed him after next year, even more focus will be on the legislature.

In one new line of attack, State Reps. Perry Stambaugh (R., Perry) and Joe Hamm (R., Lycoming) accused Nordenberg of specifically targeting them. Stambaugh, for example, would have to face another Republican incumbent in a newly drawn district that combines parts of Perry and Juniata Counties. They theorized it was retaliation for voting against funding for the university this summer, votes they took in opposition to the school’s fetal tissue research. (The funding measure still passed.)

“As a result of that vote, though, I now feel my constituents are being punished by this new redistricted map,” Stambaugh said. “For him to be drawing districts affecting people who voted against funding for his school, it seems to me that represents a huge and very big potential conflict of interest.”

Nordenberg flatly denied the charge.

“There is absolutely no truth to that claim,” he said. “Typically, when people resort to arguments of that type, it means that they have little to say about the merits of the dispute.” Nordenberg said he didn’t know the lawmakers leveling the accusation, or their positions “on any particular issues.”

Nordenberg is a registered Democrat who donated $2,000 to Joe Biden’s presidential campaign last year. He told Fox News he also donated to Republican Dick Thornburgh’s U.S. Senate campaign in the early 1990s. Nordenberg touted his “45-year record of fairness in Pennsylvania,” and said leading Republicans had encouraged him to take the commission job.

» READ MORE: Pa. Democrats could get a big boost from a new state House map, while the GOP would solidify a Senate edge

Rep. Joanna McClinton (D., Philadelphia), the House minority leader, defended Nordenberg for producing “a fair and just” plan.

“Dramatic population shifts and entrenched underrepresentation demanded a fresh perspective on mapping,” she said in a statement. “The preliminary House map is representative of the Commonwealth as it is today and allows for equal participation in the electoral process.”

But Rep. Kerry Benninghoff (R., Centre), the majority leader, said his members “were pretty stunned when they saw the maps and are reaching for rationale” because they’ve been provided no explanation for how individual districts were drawn.

“What are they supposed to think?” Benninghoff said. “Our members are left with unanswered questions, and they made the deductions they made.”

The four caucus leaders — the Republican and Democratic leaders of the House and Senate — are on the commission, and they unanimously passed the Senate map last Thursday. But the Republicans voted against the House map, with Benninghoff calling it an “extreme partisan gerrymander.”

In an interview Tuesday, Benninghoff pointed to districts he said would increase the total number of Democratic-leaning seats and reduce Republican power: “Why did you draw like that, unless the goal was strictly to give an advantage to one party?”

In many ways, Pennsylvania’s political geography inherently favors Republicans, because Democratic voters are heavily concentrated in cities and dense suburbs.

The Inquirer analysis of the map found it favors Republicans by 104 seats to 99, based on the 2016 and 2020 presidential elections. That’s significantly less of an advantage than in the current map, which has 118 Republican or Republican-leaning districts. But it’s also better for Democrats than the state’s political geography would naturally suggest.

“The map itself is a map that favors Republicans,” Nordenberg said. “It doesn’t favor them as much as the current map does, but that is a product of the changing demographics.”

Benninghoff said Nordenberg appeared to want to correct for the pro-Republican skew of previous maps. “If that is your primary focus, then you don’t want input from anyone else,” he said. “I feel like our participation was marginalized because they had a different agenda.”

Nordenberg said he listened to both leaders.

“I’m sorry that he feels that way, because I have high regard for Leader Benninghoff and feel as if we have developed a good relationship,” Nordenberg said. “We met with him as frequently as we met with any leaders.”

Nothing in the process disadvantaged House Republicans, Nordenberg said.

“This map, which continues to favor Republicans, could hardly be considered a political gerrymander,” he said.

» READ MORE: Pa. Democrats could get a big boost from a new state House map, while the GOP would solidify a Senate edge

Republicans have seized on the fact the map draws 12 or 14 Republicans together into the same district, compared with two or four Democrats, depending on the outcome of special elections. But demographic shifts mean Republican areas of the state are losing population, or growing more slowly, than the more Democratic cities and suburbs that are growing. That means more Republican districts have to grow larger in size, which Nordenberg said ensnared some incumbents.

”Inevitably, then, the process was going to bring more of them together,” Nordenberg said.

Grove, the chair of the House State Government Committee, said Tuesday that the House map violates the state constitution, which requires districts be as compact and equal in population “as practicable,” and that “unless absolutely necessary no county, city, incorporated town, borough, township, or ward shall be divided.”

He dismissed arguments that the current map was gerrymandered to favor Republicans, noting that it was supported by the Democratic leader at the time and cleared the state Supreme Court. “I don’t believe in that revisionist history,” Grove said.

Nordenberg said that the map “is a more than adequate preliminary plan” and that he welcomes legitimate challenges and further changes.

“There were issues that were raised … that are worthy of consideration,” he said of Tuesday’s GOP news conference. “And I assume that we will hear more questions of that type as we move forward.”