The Bernie Bros are vowing revenge. As the presidential campaign of Sen. Bernie Sanders continues to crash and burn, the socialist’s most hard-core supporters are vowing they will never vote for Joe Biden at the ballot box — even if that means handing Trump a second term. “We will never – NEVER boost or support Joe Biden or defend his abysmal record and terrible policy positions,” Henry Williams, executive director of The Gravel Institute, told The Post. “We will tell people, as we always have, to vote their conscience and to make decisions based on the interests of all the...