WILKES-BARRE, Pa.—When Donald Trump broke the hold of Democrats in Pennsylvania and parts of the industrial Midwest in 2016, credit went to many blue-collar, manufacturing-oriented counties that backed him by lopsided margins, drawn in part by his promise of economic renewal.

More than two years into Mr. Trump’s presidency, employment growth and other measures of economic robustness in these politically important counties have lagged behind the national trend, a Wall Street Journal analysis shows.

And...