GOP hopefuls bet on Iowa as firewall against Donald Trump

Once upon a time, the moderates, the mavericks and the underdogs in presidential politics had a chance to break through in New Hampshire.

Former Sen. John McCain, an independent-minded Republican, resurrected his anemic campaign with a victory in the state’s first-in-the-nation presidential primary in 2008. Bill Clinton, a centrist Democrat from Arkansas, became the “comeback kid” by exceeding expectations here in 1992. And little-known Georgia peanut farmer, Jimmy Carter, would go on to claim the presidency after winning the state’s 1976 Democratic primary.

But this year, New…