Story highlights For weeks, Trump has made the topic of election rigging and voter fraud a main talking point

Greeley, Colorado (CNN) Donald Trump for the second day in a row questioned the validity of this swing state's largely mail-in voting system, the latest instance of the Republican nominee expressing skepticism about the legitimacy of the electoral process.

Trump kicked off his rally here on Sunday by encouraging his supporters to "make sure" their ballots are properly counted, saying that he is a "skeptical person" when it comes to the state's largely vote-by-mail process. He then encouraged his supporters to get a "new ballot" in person at a local polling location.

"They'll give you a ballot, a new ballot. They'll void your old ballot, they will give you a new ballot. And you can go out and make sure it gets in," Trump said.

Registered voters in Colorado automatically receive a ballot in the mail, but can request a new ballot or vote in person if they have not yet mailed in a completed ballot.

"In some places they probably do that four or five times. We don't do that. But that's great," Trump said Sunday, appearing to hint at the possibility of voter fraud in Colorado, a rare prospect Trump has continued to hammer on the stump.

Read More