This is a rare case that I too could see something like blockchain, but it would have to be highly documented and transparent. e.g. What organizations and companies are running the ledgers. Who has control of what and access to what. Public confidence would have to be priority one at every step of the way. It would need something like certificate transparency, except it would have to be mandatory with attestation and validation at every step of the way and it should be possible to take the logs from any of the multiple locations and use them to prove each other real time. Meaning, even the most subtle tampering should set off alarms everywhere almost instantly and machine learning should be able to use this data and video surveillance data to show who was tampering with what and when.

People at each ledger location would have to be on a list and if found doing something malicious, heads would literally roll and the legal system would have to reflect this. There can't be one iota of "oops we made a boo-boo, sowwy". No covering up system tampering by congress. No memory-holing of system compromises like the previous mechanical voting systems. The entire system has to be capable of being audited by literally the entire planet provided they follow a bug reporting process and do not sit on discoveries.

There would be one and only one API port. Everything else is firewall restricted and monitoring on each device would look for a socket opening. The API port can be told to check for system updates and that's it. No remote management of the device. Cattle vs Pets. If a device fails it gets sent to a specific location. The device would use its own pre-shared mutual auth VPN mesh, pre-shared mutual auth on the OS and pre-shared mutual auth in the applications that update the system. A display on the box must show that this updated was triggered and by whom. Every devices must log each step of the update process to the ledger with details of who triggered the update and why and links to what changed in a public repo.

Anything short of what I described and the hundreds of millions dumped into the system would just line some pockets as the system would be deprecated like many systems before it. Public confidence would have to be priority one at every step of the way. No secrecy. No obfuscation. No classification set on anything, not even "confidential". All documents would contain the label "Unclassified". The entire planet by default gets the legal clearance of "Public Trust". 100% of the firmware, BIOS, OS and Application must be in a public repository, no exception. All binaries/blobs must be signed and checksummed. Anyone that wants one of these devices may order one from the manufacturer, minus the keys, obviously. Pen-testers have to make their own keys for their own lab.

Anyone on earth with an internet connection should be able to see real time what is being voted on and voters should be able to use a private key they generated to see their votes in action. Groups of people that wanted to should be able to see their collective votes in action.

If someone can successfully tamper with a system with proof of how they did this, they are awarded $100,000. The number of times someone may receive this award is unlimited and there are no restrictions on who may receive this award. Even members of sanctioned countries may participate. A member of congress will fly there and hand them the cash and an award certificate. If said country would perceive this as an act of war, then instead a popular youtuber would fly there and hand them the cash. These awards are deducted from the DHS and FEC budgets. If 50% of their budget is depleted, the remainder of their budget is folded into the NSA budget and their organizations are disbanded. This process repeats until there are no vulnerabilities or there are no more three letter agencies remaining at which point we move to four letter agencies.