* electronic voting machines
* credible claims of foreign interference in elections
* credible claims of organized state agent hacking of US digital infrastructure.
* voting machines with designs and source code which are secret, and no way to know if they're working as advertised.
We have cryptographic protocols for honest, verifiable, anonymous elections, which we don't bother implementing. It's all an honor system, in a government without much honor. We, quite frankly, have no way to know if votes are being counted correctly or honestly.
As much as I disbelief Trump's claims of this election being rigged by democrats, the claims that we have excellent election security are false too. We have a huge chunk of the country openly lying about election results, and another half lying about election security. Two lies don't make a truth.
If our current elections aren't being manipulated, you can bet future ones will be. It's easy for an organized state agent to do, and if it wasn't being done before, it will be now. And fixing this will be almost impossible post-Trump, because Democrats.