Democrats need a net gain of five seats to control the Senate next year, four should Hillary Clinton win. Among the most closely contested states is Pennsylvania, where Pat Toomey, the incumbent Republican, is engaged in an expensive and sometimes nasty battle with Katie McGinty, his Democratic challenger. Ms. McGinty seems on the upswing as Donald Trump’s campaign implodes, and now leads Mr. Toomey by less than a percentage point.

Ms. McGinty’s working-class roots — she is one of 10 children born to a Philadelphia policeman and a restaurant hostess — inform her advocacy. She would raise the federal minimum wage to $15 over four years, and on the whole shows far greater sensitivity to the needs of the jobless and middle-class families than her opponent.

And while she seems at times an awkward and inexperienced campaigner, she is not inexperienced in the ways of government. As chairwoman of the White House Council on Environmental Quality in the 1990s, she helped organize the Clinton administration’s successful counterattack against efforts by the Republican Congress to undermine the nation’s basic environmental laws. Later, as Pennsylvania‘s environmental chief, she helped push the state toward greater use of cleaner energy sources like wind and solar, not only as a way to combat climate change but as a source of new jobs in an aging rust-belt economy.

There were eyebrow-raising moments during her tenure in state government, as when the agency she led made grants to a nonprofit group that employed her husband, prompting stricter ethics rules. She later took a lucrative board position at an energy company she’d assisted while in state office.