The Chappaquiddick Incident Mystery

On July 19th, 1969, on Chappaquiddick Island, off the coast of Martha's Vineyard. Ted Kennedy and an aide for his brother Robert's presidential campaign careened off a bridge into the water. Ted Kennedy made it out alive, the aide, on the other hand, was trapped in the car and did not survive. What was strange about the incident was why they were driving over the bridge in the first place? Why was there an unaccounted for hour in the timeline? Why didn't Kennedy call for help? Why didn't Kennedy report the crash? How was this man re-elected for nearly 40 more years in the senate?