WASHINGTON — A lefty teacher’s campaign to knock off longtime Rep. Richard Neal in western Massachusetts is gaining national attention as left-wing insurgents take scalps across the country in primary contests — but police records obtained by The Post reveal he has a colorful rap sheet. Jeromie Whalen, a 39-year-old high school journalism teacher, was arrested in multiple confrontations with authorities — accused of a drunk assault in a hospital emergency room and then nearly driving his pickup truck into a house at 4 a.m. while also under the influence. “I’m not going to say that I haven’t made mistakes...