Doug Stanglin, and David M Jackson

USA TODAY

After warning supporters of possible election fraud in Pennsylvania, Republican presidential nominee Donald Trump invited supporters on his official website to volunteer as election observers to "Help Me Stop Crooked Hillary From Rigging This Election!"

The new page on his website provides supporters with a form to fill out to "volunteer to be a Trump Election Observer."

Speaking at a Friday evening rally in Altoona, Pa., Trump again raised the issue of possible voter fraud in the November elections, saying, "we're going to watch Pennsylvania."

"Go down to certain areas and watch and study make sure other people don't come in and vote five times," he urged his audience.

He said cheating is the only way "Crooked Hillary" could win the Keystone state, referring to Democratic nominee Hillary Clinton.

“She can’t beat what’s happening here," he told the crowd. "The only way they can beat it in my opinion, and I mean this 100 percent, if in certain sections of the state they cheat.”

Trump said he "knows the state very well" and knows Clinton "can't beat what's happening here."

Real Clear Politics, in averaging the most recent polls in Pennsylvania, shows Clinton leading Trump in the state by 9.9 points.

Jason Miller, a campaign spokesman, said in a statement that elections observers "will help ensure lawful voters can vote."

"To be clear, liberals love to throw out the voter intimidation card," Miller said. "What we're advocating are open, fair and honest elections."

He said poll watchers are a standard part of the voting process, and many states permit campaigns to have credentialed observers.

"It is standard for campaigns to recruit volunteers for this in advance of the election," he said. "We had them in the primaries as well. Most campaigns do, and many jurisdictions offer guides."

In 2014, a Pennsylvania judge struck down a law requiring voters to produce state-approved photo ID in order to vote.