Though there is already plenty of evidence of "irregularities" and "errors", nearly all of which favoring Trump, in key swing states, and even some evidence of possible machine tampering in Wisconsin, the truth is that tampering and hacking are really NOT the biggest problems in terms of potential election rigging. As author and pundit Greg Palast notes, much, much larger are the problems of voter suppression, discarded votes, and related systemic issues that worked in Trump's favor. Such problems tend to be far more prevalent in Republican-controlled states, and (not coincidentally) tend to disproportionately disenfranchise people of color and other voters who are statistically likely to vote Democrat. And most of it is effectively legal.
Note that Republicans are always the ones who push for suppressive and overly stringent voter ID laws, which are basically a solution in search of a problem given that in-person voter fraud is much too rare to have meaningfully affected any election thus far. They even repeat the same tired, old debunked canards about illegal immigrants and dead people voting in order to justify both voter ID laws as well as other suppressive measures like Crosscheck, a computer which is used to purge "questionable" voters from the election rolls. And purged voters who find their names mysteriously missing on the rolls are either turned away or, if they request it, given "provisional" ballots that all too often end up in the trash and are thus "placebo" ballots. Also, many states permanently revoke the right to vote from convicted felons even after they have paid their debt to society--and due to institutional racism, this disproportionately affects people of color. Add to this the fact that poor people and people of color statistically tend to get the worst voting machines (i.e. more likely to malfunction) at their polling places, voter intimidation, and stuff like that, and you have a recipe for massive disenfranchisement of likely Democratic voters. And make no mistake, none of this is any sort of accident, this is all by design.
And since the Supreme Court essentially gutted the Voting Rights Act in 2013, things have only gotten that much worse since. That was done despite common knowledge that racial gerrymandering and voter suppression of people of color would most likely increase as a result of such safeguards becoming unenforceable in practice.
So yes, the 2016 election was rigged, even if there was no tampering. Just like every election before it, to one degree or another. And it was rigged in favor of the party of the privileged, which is none other than the GOP. After all, as Greg Palast famously said, America is "the best democracy money can buy".