I often say that election security is by far the hardest technical problem I've ever encountered. Why? Four reasons:

1) Contradictory critical requirements, particularly vote secrecy vs. transparency.

2) No truly neutral trusted third parties.

3) Election do-overs are generally impossible, so the ability to merely detect problems is insufficient. You have to reliably prevent them.

4) Much of the technology than can manage the complexity of elections is inherently untrustworthy.