But you have to admit, Ferning, that the original argument that "the conspiracy is so perfect that there is no credible proof right now that it happened, although we know it did" holds even less water, and is flexible enough to be used to prove anything from election fraud to Obama being born in Kenya to Donald Trump being a reptilian alien from the 10th planet of our solar system (the 9th planet also being covered-up). 
The argument, such as it is, appears to be that certain types of scenarios will have an identical appearance despite two potential histories. This is not particularly controversial as far as I'm concerned. It's quite evident that not all observations can lead to a back-trace of history; that does not discount that multiple histories are potentially possible. An example that actually sees considerable play in the real world is that of the existence of God. If you on the one hand take a universe with no God, and on the other hand one where God does not materially interfere like a wizard, or if He does it's in invisible ways, the two are going to be appear isomorphic if you look out the window and do a general inspection. It does not mean that the lack of being able to tell the difference at a glance means you have derived some kind of information about which situation you're in. It actually means that if you're being rational you have to be agnostic until you receive more on the subject. Now in terms of campaign fraud I suppose this might mean accepting that it could be true while also knowing it could be impossible to find out. The issue here seems to be largely about money - how much is it worth to construct a system from whole cloth that would avoid this potential issue, especially considering it may not even be happening?
The issue is not so much about money, but the fact that, given the premise, any statement can be "proven" true. Which therefore means that it proves nothing.
But then I wouldn't have expected any less from a reptilian alien.
And while the Manhattan Project was well concealed at the time, it eventually was uncovered, and it was a much simpler operation to keep undercover, since it occurred in a small location with a limited number of people who were involved.
The totality of the project actually included huge amounts of people. But what would be true would be to say that very few of them knew the full significance of what they were doing. And the same would presumably be true of a voter fraud situation, if it did exist.
Except a lot of them, if not all, knew they were doing something secret, and quite a few of them probably guessed something about what it was, especially when reports came out about what was really happening. And practically all of them knew they had to keep quiet because there was a war going on. Basically, the people involved were told they were doing something that had to do with national security and agreed to keep quiet.
It would be a very different situation for massive voter fraud. People would have to ignorant of what they were doing or that it would be considered illegal (highly unlikely if they were competent at their jobs or reasonable intelligent), or agreed to keep quiet about it, even though there is no national security issue with what they were doing, it is actually illegal and could cause they harm if they did not report it, and there are widespread "reports" of it happening. In other words, rather than being patriots and help defend their country, every single one of them would know they were hurting their country (or believe it was best for the country, in spite of being illegal), or just be stupid.
When you have the entirety of the U.S. laws and government, and the will of the people, behind you, it is possible to keep a grand secret like the Manhattan Project (mostly) secret. When the laws and the U.S. government are against you, along with at least half the population, it is nearly impossible to keep everyone to that level of secrecy.
