The value of the popularity of maverick campaigns such as those of Sanders and Donald Trump is not that either candidate is particularly wonderful, but that political dissent is growing and people are hungry for alternatives. By David A. Fahrenthold Washington Post Greg Guma, who worked with Bernie Sanders and later wrote a book about him, shows off old articles and photos. (Jabin Botsford/The Washington Post) BURLINGTON, Vt. — It was one of the first political events Bernie Sanders ever went to in Vermont: a 1971 discussion by a small group of left-wingers, the Liberty More…