DERRY, N.H. — A key to understanding the 2016 U.S. election lay beneath the stage where two of its principal antagonists were standing the other night. Two storeys below the hall where Democrats Hillary Clinton and Bernie Sanders last debated, there's a museum display chronicling the de-industrialization of Derry, N.H. It shows machines from old shoe factories that have disappeared, supporting jobs that have disappeared, held by people now disappearing: well-paid, low-skilled American workers. The local historian who runs it recalls a once-bustling main street. It's filled today with a high-end shop here, a pawn shop there, and an empty storefront or two in between. "Gone, with the middle class.'' "These were all factories. Shoe factories. Gone,'' Rick Holmes said, gesturing at the street. "Gone, with the middle class.'' New Hampshire clearly counts as an economic success story. It's among the richest states. It has a microscopic unemployment rate of 3.8 per cent. But pop open the hood and underneath those numbers you'll find the same engine powering the discontent now threatening to overrun the establishment of both political parties. This state has bled middle-class manufacturing jobs, like much of the country. And the two insurgent candidates who could win Tuesday's primary have seized upon that sense of loss. Donald Trump and Bernie Sanders are leading big in New Hampshire polls, to the mortification of a political establishment that has derided both as unelectable.

Donald Trump, Republican presidential candidate, speaks during a campaign rally at Plymouth State University in Holderness, N.H., on Sunday. Trump, far from humbled by a second-place finish in the first presidential nominating contest, bet again on his forceful personality as he battled a combative audience in New Hampshire just days before the state's crucial first-in-the-nation primary. (Photo: Andrew Harrer/Bloomberg via Getty Images) The rumpled socialist and the bewilderingly coiffed billionaire may be different personalities, with different worldviews, proposing different solutions. But they're pointing to the same problems, real or alleged: trade deals, decent jobs shipped overseas or replaced with machines, and an indifferent political class distracted by the priorities of its mega-rich campaign donors. "They both come across as angry men. And I think many of their voters are also angry.'' Sanders' proposed fix? A drastically expanded social-safety net: free college tuition, Canadian-style health care, and paid parental leave. Trump's? Kick out millions of illegal migrants from Mexico, who work under-the-table for cheap salaries. And protect existing social programs. They have one major policy in common: ripping up trade deals. Holmes predicts they'll do well Tuesday. "They both come across as angry men. And I think many of their voters are also angry,'' he said. "They're frustrated, trying to balance the family budget.''