As I recall, Clinton enjoyed a significant RISE in the polls after Comey announced that her conduct with respect to the unsecured servers was "extremely careless" but should not be prosecuted -- even though the servers contained a number of classified documents. Prior to the then there had been concern among many American voters that voting for Clinton might mean voting for someone who might shortly be facing prosecution. Only after Comey's second announcement regarding the discovery of possible NEW emails on Weiner's unsecured server (Weiner being the estranged husband o one of Clinton's closest aids) did Clinton appear to suffer negative consequences, although even before then Trump was closing in on her, according to the polls. Arguably, Comey's first announcement promising no prosecution hurt Trump more than Comey's second announcement hurt Clinton.