Story highlights Donald Trump says Republican leaders are "very concerned" about cheating

Recent polls show Hillary Clinton with a 10-point lead in the state

(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.

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