When Trump speaks of vote rigging he's intending voter suppression, especially blacks. No big secret. I suspect that until he met with Karl Rove months ago he was ignorant of computer vote flipping; and that virtually all computer vote counting is done on Republican controlled companies which are routinely strategically manipulated. (See Professor Mark Crispin Miller's recent compilation of the evidence. http://markcrispinmiller.com/2016/11/election-theft-a-conspiracy-theory-only-an-ignoramus-or-a-troll-would-say-so-heres-the-evidence/)
One dramatic example of such flipping I've cited in the past is the theft of the 2002 election from Don Siegelman for governor of Alabama. It was a close race and one county reported a set of results from electronic machines that made Siegelman governor. Then in the middle of the night the computers recalculated and reported a different set of results. He lost the race. (He now sits in jail, afterwards railroaded by Karl Rove and his cronies. President Obama refuses to pardon Siegelman, nor did the White House make any effort to intervene to keep him out of jail in the first place.
Computer vote flipping to reverse election results on a state and local level goes back to the 90s if not before. On a national, presidential level I'm not aware of such interventions till 2000 when the votes in Florida were flipped to give the race to George W. Bush. In 2004 the flippers learned their lesson and they made sure it wouldn't be close and they gave the national vote to Bush as well as shifting the electoral college. Is it amazing that they could get away with giving the election to someone who was so deeply unpopular after four years in office, not least because of Iraq? Kerry was well aware that Ohio was stolen but he turned out to be one of a long line of Democrats who didn't want to be president. He apparently was also briefed on the the long planned US attack to retake Falluja which would have to be indefinitely postponed if he contested the election.
Needless to say the major media – as well as the left alternative media – are unwilling to report on such high level hijacking of a presidential election. One symptom that they prefer to look the other way is that is that they refuse to engage in exit polling in critical areas which would reveal the discrepancy between official results and how people actually voted.
Interestingly, a similar high profile signal of election rigging happened in two presidential elections -- in 2012 and in 2000. In 2000 Florida was so clearly won by Gore that the TV media were calling it for the Democrats by around 10 pm. Soon a surprise national interview was granted by the Bush family as they watched the results on TV in their hotel room. The Bush spokesperson warned that no matter how clearly the results in Florida seemed, the Bush camp were still confident it would change in their favor. In hindsight, we can deduce that that they preparing the country for a contested election, not to mention that the fix was in.
On the evening of the 2012 election, despite the overwhelming numbers, Karl Rove also tipped his hand that he had intended to reverse a potential Obama victory. Search: "Karl Rove's election night melt-down on Fox News." On national TV he kept insisting that it wasn't over, that late results would swing the race to Romney.
For the latest iteration in computer vote flipping see http://blackboxvoting.org/fraction-magic-1/