"The death of US Senator Edward Kennedy marked the twilight of a political dynasty, and dealt a blow to Democrats as they seek to answer President Barack Obama’s call for an overhaul of the healthcare system. Kennedy had made healthcare reform his signature cause." - SCMP(Aug 26, 2009)
Dear teachers, I would like to know why the death of E. Kennedy will dealt a blow to Democrats on the revamp of the US's healthcare system, and what the "signature cause" means. Thank you for your help.