(CNN) Donald Trump and his campaign are increasingly casting doubt on the legitimacy of the presidential election.
The Republican nominee declared Friday there's only one way he could lose the state of Pennsylvania: if he's cheated out of it.
"We're going to watch Pennsylvania. Go down to certain areas and watch and study and make sure other people don't come in and vote five times," he said at a rally in Altoona. "If you do that, we're not going to lose. The only way we can lose, in my opinion -- I really mean this, Pennsylvania -- is if cheating goes on."
Then on Saturday morning a Trump spokeswoman detailed the campaign's concerns.
In an interview with CNN's Victor Blackwell, Trump spokeswoman Katrina Pierson said the campaign was concerned with potential election fraud, particularly over electronic voting machines, which security researchers have warned are vulnerable to hacking.
Trump has offered no evidence to back up his claims that the elections would be "rigged" against him, and asked about making an unjustified assertion, Pierson said it was a concern over a hypothetical scenario.
"There is no evidence because the election hasn't occurred yet." Pierson said. "This is not far-fetched. Election fraud has been a concern for a very long time."
The Trump campaign went still further, calling on its website for supporters to volunteer to be Trump election observers.
"Help me stop crooked Hillary from rigging this election," the site reads.
After signing up to become a "Trump Election Observer," the user is redirected to a donation page.
Although Trump's claims about electoral fraud may be unprecedented for a national politician in the modern era, the Republican Party has faced legal pushback in the past for its attempts to have poll watchers similar to what the Trump campaign is now requesting from its supporters.
Trump on Friday said Republican leaders in Pennsylvania "are very concerned" about the possibility of cheating -- adding, "We have to call up law enforcement, and we have to have the sheriffs and the police chiefs and everybody watching."
Hillary Clinton's lead in the polls in Pennsylvania is solid -- a Quinnipiac survey of likely voters released Tuesday found Clinton leading Trump 52% to 42%. But both candidates are devoting significant resources to the state, which has a base of working class voters that Trump's campaign hopes could work in his favor.
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Trump, who campaigned earlier Friday in Erie, Pennsylvania, said he "knows the state very well" and knows Clinton "can't beat what's happening here."
Unless there's cheating.
"The only way they can beat it, in my opinion -- and I mean this 100% -- if in certain sections of the state, they cheat," he said.
Trump's latest moves echoed -- but went even further than -- his statements last week in Ohio that he's "afraid the election is going to be rigged."
RELATED: Trump: 'I'm afraid the election's going to be rigged'
Pennsylvania does not require voters in the state to show photo identification -- which Trump said he finds "shocking."
Ben Carson, who supports Trump, told CNN's Erin Burnett that the focus should be on how to make sure there is no voter fraud -- which he noted would be good for both parties. He also acknowledged he might not have used the words as Trump, his former Republican primary rival.
"I would've said it in a different way. I would've said, 'There have been some irregularities and we want to make sure that those don't occur.'"
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At his first rally on Friday, Trump put his dislike of the media in harsher terms than usual -- calling journalists "the lowest form of life."
"I tell you, the lowest," he said. "They are the lowest form of humanity."