voting is a bottom-up process; it happens in precincts in cities in counties in states, there are too many local levels for high-up party leaders to easily orchestrate a nationwide rigging operation and too many people to corrupt. it's not impossible that foul play could happen, but the amount of resources required to make any reasonable dent in electoral numbers is very slim
the electoral process for the president is also not direct. the majority of states are strongly affiliated with one party and all of their electoral votes will go to the party which wins a plurality in that state. in order to maliciously push the outcome of a red state in favor of the democrats, you would need to rig enough votes to win over the plurality in that state. which is to say, in a heavily red or blue state, that isn't happening.
in a swing state, however, maybe you have a chance. so let's take florida. in
2012, florida had a voter turnout of around 57% of the voting-age population (15,839,713). rounding that up to 60%, we can say that around 9,503,827 florida citizens voted in the 2012 presidential election. obama won florida by
74,309 popular votes. that means to shift the plurality in romney's favor, the republican party would have had to rig 74,310 votes, and if we're saying this was done by physically bussing people around to different counties, then it'd be pretty insane to think that
nobody would notice seventy five thousand people committing en-masse voter fraud. in other swing states, this number grows,
in iowa it'd be 91,927,
in colorado it'd be 137,858.
it's definitely not impossible that this happens, but it's so highly improbable that i'm unconvinced anyone has the power to really make that much a difference. we're assuming massive rigging movements across the nation orchestrated by party authority, and the only power higher up party leaders really have over local leaders is money, and this is money that i don't think exists. i'd be willing to believe that fraud is happening and that some people are trying to play the system, but it's highly unlikely that anyone is able to inconspicuously pull off any conspiracy of significant scale. and as with all conspiracy theories like this, we're supposed to believe that the hundreds of thousands of people that would be involved in this process over apparently many decades have all just stayed quiet; that nobody would have ever come out about this corruption after all this time. i'm not sure i buy it.