Donald Trump's effort to cushion the landing of what increasingly looks like a large electoral loss goes something like this:
1. Reject polling as inaccurate. The guy who spent five minutes in every speech from July 2015 to March 2016 talking about his poll numbers has recently begun disparaging what the same pollsters see now. At times Trump offers a vague "this is a movement" explanation for why the pollsters may be missing something; at other times, he and his team imply bias.
Trump's goal? Make the race seem closer than it is.
2. Imply that voter fraud is rampant and substantial. Trump's meandering description of the election as rigged offers different villains on different days: Sometimes it's the media, sometimes it's House Speaker Paul Ryan, oftentimes it's Hillary Clinton. But he also frequently points to supposed voter fraud, a claim for which there's no evidence now and for which there's never been any evidence on a large scale. You can see how this plays into the first point: If people think that the vote is close but Clinton ends up winning big, clearly something untoward happened.
Trump's goal? Make a Clinton victory seem suspect.
But what happens when, on Election Day, there isn't obvious evidence of fraud? When exit polls conducted with voters show an overwhelming preference for Clinton (if that should happen)? Well, you're just going to need to have your own folks out there digging up fraud. And you're going to need your own exit polls.
Trump's campaign is already planning on the former. They've been signing people up to be "election observers" since August, asking people to go to poll sites and keep an eye on things. From a political campaign standpoint, this is an unwise way to use volunteer resources: Instead of contacting or turning out voters, you're getting people to keep an eye out for ghosts in places near where they live — which are probably therefore more Trump-friendly anyway. If the Republican Party gets involved, it's even more problematic. Under a long-standing consent decree, the GOP is prohibited from participating in programs that aim to intimidate voters.
That's pretty clearly what Trump's effort would result in: his supporters challenging voters at the polling place. One Trump supporter explained to the Boston Globe how he saw it working.