When it came time to recruit candidates for next year’s midterms, some Democrats had a goal of finding political newcomers who don’t talk like Beltway insiders and are ready to fight back against the Trump administration. As the saying goes, be careful what you wish for. U.S. Senate candidate Graham Platner of Maine, a gruff veteran turned oysterman, seemed to fit the bill: marrying left-leaning policies with the blunt talk of the blue-collar men Democrats have been hoping to win back. Some in the party fell in love. Others thought that two-term Democratic Gov. Janet Mills, who jumped in the...