Donald Trump has a problem no matter what happens in New Hampshire on Tuesday night: There’s a whole swath of the Republican electorate and a good chunk of independents who appear firmly committed to not voting for him in November if he becomes the nominee. It’s an issue that became starkly apparent in polling ahead of the Iowa caucuses‚ when an NBC News/Des Moines Register/Mediacom poll of voters in that state found that fully 43 percent of Nikki Haley supporters said they would...