When Donald J. Trump landed in Pittsburgh a few weeks ago, the city was buzzing about Uber’s deployment of the world’s first fleet of driverless taxicabs. Political leaders were thrilled that Silicon Valley was hiring highly paid workers and investing hundreds of millions of dollars in western Pennsylvania. Local taxi drivers were understandably less excited that robots were coming for their jobs.

Pittsburgh’s football team may still be called the Steelers, but the city has, like the rest of the country, become predominantly a service economy. More than 80 percent of local jobs are in the service sector, roughly on par with the national average. The largest private-sector employer is not U.S. Steel but the University of Pittsburgh Medical Center. The city’s jobs, however, increasingly are divided between a prospering college-educated elite of lawyers and doctors and bankers and a struggling mass of fast-food workers and security guards and nannies.

Uber’s arrival suggests those disparities are likely to intensify. The com­pany says it plans to create a total of 1,000 high-paying jobs at a Pittsburgh research center, presumably with the goal of eliminating the region’s 1,360 taxi-driving jobs. That may be a good deal, in the end, for the regional economy: Workers earning higher wages are also consumers who spend more money. But the trade-off would be little comfort to drivers, who are unlikely to move from that job to programming robots. And cabbies aren’t the only ones with cause for alarm. Self-driving vehicles presumably will also begin to replace the region’s 19,490 truck drivers and 9,390 bus drivers.

The Republican presidential nominee had not come to western Pennsylvania to talk about any of that. He looked out over his audience and promised, as he does at most of his rallies, that he would revive the American steel industry.