Down-and-out Youngstown, Ohio, last year became emblematic of the power of Donald Trump’s campaign. With his populist message targeting white working-class voters, he outperformed every GOP nominee since Richard Nixon won the Democratic stronghold of Mahoning County.Today, the blue-collar town represents one of the looming challenges of Trump’s presidency, six months in: how to keep the support he won as a populist candidate, when he flipped disgruntled Democrats and independents to his side of the ledger, while in many cases governing like a plutocrat who has so far failed to deliver on many of his campaign promises.Trump will test the waters Tuesday night when he takes the stage in Youngstown at the Covelli Centre, a large arena that typically hosts events like ice hockey, WWE wrestling matches, and monster truck tours.