Significant wording, this.
Trump's clearly seeing that the tea leaves aren't reading in his favour. Despite all his talk about winning so much, he could very well be about to lose big.
So, he's framing. If he loses, it won't be that the American people rejected him, but that the election was rigged. How else could he lose when he's clearly the best, smartest, longest-fingered dude with the most sacrifice/success/hot women on the planet?
It's his victory, period - and if he doesn't win, well, someone had to have taken that victory from him, right?
So here's the big concern that has to be on Homeland Security's mind. Let's say Trump tells his supporters that the election was stolen from him using some of the rhetoric he's used in the past. Maybe he doesn't tell them to fight back against the system and put him in power - but maybe he just says some things that, when each word is connected to the next, kind of insinuate that.
Trump has a lot of angry, gun-owning people in his base. There are white supremacists and other bigots who see this as their moment and might be just as angry to see it taken from them.
Remember that failed coup in Turkey?
We know who could trump that.