As a warrior, one of our most crucial tasks is... protection. We are the shield of the Horde, and we keep our weaker brethren safe. If you are to join in our ranks, then you must prove your mettle to me. -Veteran Uzzek
There has been extensive review of this and there is no evidence of wide spread voter fraud, just more bull spread by Trump.
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Some of the foremost expects is computer security have already said that the voting machines regardless of not being connected to the internet are quite susceptible to tampering.
I understand many Trump supporters don't believe experts in any field or of fact and evidence, but these things can't really be disputed.
Using voting computers (they are not mechanical machines, they are programmable and therefore can be manipulated) has been widely criticized by IT-Sec researchers since the idea first came up. There are so many possible scenarios for tampering, from changes in the software to more profound tricks like messing up the calibration of the touch screen by just enough to make some of the button presses register wrong.
Combine that with the fact that there is apparently a severe lack of regulation on a federal level in terms of the required technical specifications for voting computers, some of the models used this election don't even produce a paper trail which makes it almost impossible to do a proper recount.