The 2016 was the perfect storm of shit, can't put it all on Comey, all though he did screw the pooch at the end.
You also had to down to the DNC backing her regardless of how horrible she was seen, you have her actions with Sanders and just how smug and entitled she acted like she didn't need their votes up until near the end, have the email leaks, have her refusal to campaign in many places thinking she was owed their votes, had them ignoring the fact that Trump was actually talking about problems and they weren't really doing the same in many of them.
Comey was the straw that broke the camels back, but he wasn't the only straw there by any measure.
Edit: The DNC knew what was up with all the Benghazi crap. They should have just let it all play out, and then have her run in the primary only to resign part of the way through having the Republicans blowing all that time and money for someone to just take all the heat till then and bow out.