CHICAGO — Darnell Williams might be one of the most experienced convention goers at the Democratic National Convention this week, with seven under his belt. The Massachusetts delegate, who works with the Massachusetts Department of Transportation, first attended a Democratic convention in 1980 when he supported Sen. Ted Kennedy, the intra-party challenger to incumbent President Jimmy Carter, who would win the Democratic nomination but ultimately lose to Republican Ronald Regan. ALSO READ: Donald Trump exploits AP photo error for new $99 ‘Save America’ book Want more breaking political news? Cl…