If the machines aren't connected of course you need access to a lot of machines to have any effect on an election.
All machines are hackable all systems are hackable. But focusing on the box showing you can hack that changes absolutely nothing about the overall threat of the US election being hacked. No one with serious technical understanding would claim that it was impossible to hack the boxes. And so you are back to a much harder task which is the social engineering part of convincing thousands of people to betray their country and no one finding out.
To alter the results in a cheaper way than with traditional vote stuffing methods, as recently observed in the Turkish national referendum. https://arxiv.org/abs/1706.09839
All machines are hackable all systems are hackable. But focusing on the box showing you can hack that changes absolutely nothing about the overall threat of the US election being hacked. No one with serious technical understanding would claim that it was impossible to hack the boxes. And so you are back to a much harder task which is the social engineering part of convincing thousands of people to betray their country and no one finding out.