Pavarotti himself couldn’t sing such praises as President Trump has lately been warbling in respect of the Gilded Age. We share the sentiment. “We were at our richest from 1870 to 1913,” he exudes. Mr. Trump marks the role of tariffs in the triumph, and there’s no doubt that they featured in America’s rise to global glory. Yet Mr. Trump overlooks another, even more crucial aspect of Gilded Age economics — America’s strong and stable dollar, good as gold.