MONACA, Pa. — The hulking petrochemical plant is being constructed 30 miles from his city, but Pittsburgh Mayor Bill Peduto worries it's just the sort of polluting industry that could threaten residents' health and drive away the white-collar jobs of the future.

"If there is one city in the United States that should have learned from the mistakes that it made in the previous industrial revolution, it's Pittsburgh," Peduto (D) said.

But here near the developing complex on the banks of the Ohio River, local Democratic official Earl “Butch” Shamp looks downstream at Peduto and sees the kind of politician he says is killing the Democratic Party in large swaths of southwestern Pennsylvania.

“When people here hear the mayor, they hear someone who’s just totally out of touch about where the jobs are,” said Shamp, the lone Democrat on the Potter Township Board of Supervisors in Beaver County, where the plant is located. “The mayor should just stay out of it and stay in Pittsburgh.”

Royal Dutch Shell’s giant petrochemical facility, which will “crack” natural gas molecules to produce a component for plastics, is also exposing a crack in Pennsylvania’s Democratic Party. For some, like Peduto, the project is an environmental menace that undercuts the party’s climate change agenda.

For others, like Shamp, it is a catalyst for a region’s economic revival and an opportunity to win over a white working class that believes Democrats have prioritized social issues over their financial prosperity.

With Pennsylvania expected to be a crucial battleground in the 2020 presidential contest, the local fissure is highlighting a national dilemma for the Democratic Party as it tries to address the environmental demands of liberal urban activists while reaching out to voters who rely on the manufacturing industry for jobs.

The party’s failure to find that balance proved fateful in 2016, when blue-collar voters in the counties that surround Pittsburgh abandoned Democrats in droves, and Donald Trump carried the state by about 44,000 votes.

“In Pennsylvania, everything matters right now” politically, said Christopher P. Borick, the director of the Muhlenberg College Institute of Public Opinion. “This is certainly not where Democrats want to be, in terms of finding a unified voice in a key swing state ahead of 2020.”

The petrochemical plant has become a political crucible. President Trump visited the Shell site in August, speaking for more than an hour while surrounded by construction workers and touting the complex as “one of the single biggest construction projects in the nation . . . made possible by clean, affordable, all-American natural gas.”

For Trump’s political rivals, Peduto has upped the ante by tying his potential endorsement to where the candidates stand on environmental matters. He has reached out to the campaigns of former New York mayor Mike Bloomberg and former South Bend, Ind., mayor Pete Buttigieg, hoping that they back his vision for more government funding for green industries.

Peduto said he is leaning toward Bloomberg and Buttigieg because the energy policy positions of Sens. Bernie Sanders (I-Vt.) and Elizabeth Warren (D-Mass.) — who support a ban on fracking — “would be devastating to the Rust Belt.” Conversely, Biden’s positions, he said, “are more like Donald Trump’s than they are a pragmatic approach toward the middle.”

Shell’s 400-acre facility relies on Pennsylvania’s vast reserves of natural gas, obtained by fracking shaleto produce ethylene, a component of plastic that is used for various consumer products, from food containers to furniture.

Its construction has generated 6,000 jobs already, and it is slated to employ 600 permanent workers when it opens in the “early 2020s,” according to the company. Industry leaders and state officials say the area around the plant could turn into a hub for the petrochemical industry, producing more jobs, with tentative discussions about a half-dozen additional petrochemical facilities in nearby communities in Pennsylvania, Ohio and West Virginia.

Worried about western Pennsylvania becoming the next “chemical alley,” Peduto shocked many observers in October when he called for a moratorium on cracker plants, against the wishes of corporate and labor leaders.

The Shell plant is licensed to produce up to 1.6 million tons of polyethylene annually, a process that could involve emitting up to 522 tons of volatile organic compounds and 348 tons of nitrogen oxides annually. Peduto said those emissions are equal to adding 450,000 vehicles to ­Pittsburgh-area highways, severely undercutting the city’s goal of being carbon neutral by 2030.

Peduto, who is in his second term, also worries that the plant will make it harder for him to attract and retain the medical and technology jobs that power Pittsburgh’s economy.

“We have to be able to recognize that there is a new industry that has been built out in southwestern Pennsylvania, and it is contingent upon clean air and clean water,” Peduto said, citing Uber’s and Microsoft’s recent investments in the region. “And that industry is much more important than the legacy and industry of fossil fuel.”

The blowback from other Democrats has been intense. Pennsylvania Gov. Tom Wolf publicly broke with Peduto on the issue, saying that the region cannot flourish economically without capitalizing on its natural resources, which he thinks can be done in an environmentally responsible way.

“We have to do it right, but we have to do it, or we are not going to have the future that we deserve,” Wolf said in an interview. “I think you need the jobs of technology, which Pittsburgh has, but I think you need to take advantage of your natural attributes, one of which is natural gas.”

Shell said it has taken steps to minimize the complex’s environmental impact.

“We designed our Pennsylvania facility to obtain the lowest achievable emissions. That includes deployment of the best emissions control technologies available and one of the nation’s most stringent leak detection and repair programs,” the company said in an emailed statement.

Peduto’s position is in line with his constituents’ evolving politics. Since Trump’s election, Allegheny County, which includes Pittsburgh and its immediate suburbs, has moved to the left politically, with Democrats flipping two state Senate seats and one seat on the county council.

Two democratic socialists, Sara Innamorato and Summer Lee, also unseated incumbent Democrats in state legislative races in Allegheny County after they campaigned on environmental issues, including opposition to fracking.

“Citizens are finally saying, ‘We’ve had enough climate change, and we’ve had enough air pollution, and the last thing we want is the region to be inundated with even more bad air,’ ” said Matt Dixon, a Pittsburgh environmental activist.

Despite those recent Democratic gains in Allegheny County, the rest of southwestern Pennsylvania has continued to move to the right. Last year, Republicans seized control of four county boards in historically Democratic areas.

Pennsylvania Republicans predict Peduto’s environmental views will drive even more voters away from Democrats this year.

“This is a guy who put together a $9 billion tax credit plan to try to lure Amazon, but yet he wants to toss these jobs away?” said Allegheny County Councilman Sam DeMarco III (R), referring to Pittsburgh’s unsuccessful effort to lure Amazon’s planned East Coast headquarters. (Amazon founder and CEO Jeff Bezos owns The Washington Post.)

In Beaver County, Shamp said Democratic residents feel Peduto cares more about “building bike lanes” than workers’ ability to feed their families.

“Democrats have just gone way, way too far to the left,” said Shamp, 61, who voted for Trump in 2016 and probably will again. “I don’t believe in global warming. . . . I believe the Earth goes in cycles, and we just happen to be in a warming cycle right now.”

Residents who live in the river towns near the plant say the local economy has dramatically improved since construction of the plant began in late 2017.

Unemployment has fallen to about 5 percent, approximately half of what it was a decade ago. Residents have seen the construction of several new motels and are eagerly awaiting the opening of a popular Pittsburgh dining staple, Primanti Brothers, which is known for heaping french fries onto thickly sliced sandwiches.

“After all of these years of people talking about the steel mills closing and crying about that, there are now ‘help wanted’ signs everywhere,” said Ed Becker, owner of Bowser’s Restaurant, where customers can get a pound of spaghetti and two meatballs for $6 on Thursdays. “Actually, they have to put ‘help wanted’ banners up — it’s not even a sign anymore.”

In Vanport, a small town that sits across the river from the plant, Margo Collins said her neighbor’s house is on the market for $220,000 — more than double what she bought her similarly sized house for five years ago.

Collins, 54, who described herself as a lifelong Democrat who now supports Trump, said that kind of economic benefit makes it hard to consider the plant’s effect on her health and the environment.

“Of course, it’s going to affect the atmosphere and ozone, but to what degree? Who knows,” Collins said. “We’ve been living with it since the Industrial Revolution, and we’re still here.”