Machines aren't necessarily the problem. It's the lack of transparency and security. For a high level of confidence I believe it would have to be an open-source network where many nodes, such as at least one node from each county, can verify that all other nodes are behaving properly. More stuff too, but that's a good start. Dominion is a black box system where there's virtually a 100% chance that some are regularly being manipulated by insiders or outsiders.