Caro covers this pretty extensively in his LBJ biography series, but it's reasonably clear from the evidence that LBJ won his senate seat by some pretty crude paper voting record manipulation after the fact - changing a '7' to a '9' by writing over the number with a pen - almost certainly with LBJ's knowledge. Given that his senate seat eventually put him in the presidency, it's probably the most consequential voter fraud ever committed in American history (that we know about, I suppose).
Caro covers this pretty extensively in his LBJ biography series, but it's reasonably clear from the evidence that LBJ won his senate seat by some pretty crude paper voting record manipulation after the fact - changing a '7' to a '9' by writing over the number with a pen - almost certainly with LBJ's knowledge. Given that his senate seat eventually put him in the presidency, it's probably the most consequential voter fraud ever committed in American history (that we know about, I suppose).