By the old formula, Mrs. Clinton should have prevailed. But these counties — some of which are 98 percent white — tilted the state to Mr. Trump. The totals in any one of them may seem small, but in the aggregate, they gave Mr. Trump a margin of victory at least 150,000 votes bigger than Mr. Romney had run up four years earlier. That was enough for Mr. Trump to win Pennsylvania and its 20 electoral votes by a razor-thin 48.58 percent to 47.85 percent.

“I’ve heard people lay the blame on the African-American community not supporting Hillary strongly enough, but I don’t buy it,” Terry Noble, the chairman of the Pennsylvania Democratic Party’s rural caucus, told me. “Rural Pennsylvania went crazy for Trump. They literally came out of the hills.”

In the lead-up to this November’s election, there has been a focus on the suburbs. If you listen to cable news for any length of time, you’re likely to hear some pundit say, “It’s all about the suburbs.”

Mr. Trump’s 1950s-sounding appeals to “suburban housewives” — as well as his racist pitch that Mr. Biden will flood their pleasant neighborhoods with low-income housing — accentuate the feeling that the suburbs are what matters most.

But if the election is close again, rural voters — not just in Pennsylvania but in other battleground states — may decide its outcome.