Graham Platner, a scandal-plagued Democratic Senate nominee whose insurgent rise had drawn comparisons to Donald Trump, ended his campaign on Wednesday after a rape allegation threatened to derail one of his party’s best chances of flipping a Republican-held seat.Platner, a Marine veteran, oysterman and political newcomer, won last month’s Democratic primary in the northeastern state of Maine to face Republican Senator Susan Collins in November’s midterm elections.His withdrawal gives Maine...