The average of the major opinion polls showed Clinton with a 6-7% lead over Trump before Comey's letter became public but this dropped to 2-3% afterwards. The latter polls very accurately predicted Clinton's lead in the final popular vote total. Since Trump won each of Michigan, Pennsylvania and Wisconsin by 0.2% to 0.7%, it is clear that, without Comey's letter, Clinton would have won these three states (and possibly Florida) and would be President today. This doesn't excuse the very poor campaign that she ran but does suggest that Comey should feel nauseated.