Donald Trump speaks in Altoona
Donald Trump speaks in Altoona
Now playing
02:19
Trump: If Clinton wins Pennsylvania, she cheated
PHOTO: TV3
Now playing
01:01
Clinton: Children treated as political pawns
AUSTIN, TX - NOVEMBER 17:  Former U.S. Secretary of State Hillary Rodham Clinton signs copies of her new book 'What Happened' at BookPeople on November 17, 2017 in Austin, Texas.  (Photo by Rick Kern/WireImage)
PHOTO: Rick Kern/WireImage/WireImage
AUSTIN, TX - NOVEMBER 17: Former U.S. Secretary of State Hillary Rodham Clinton signs copies of her new book 'What Happened' at BookPeople on November 17, 2017 in Austin, Texas. (Photo by Rick Kern/WireImage)
Now playing
01:01
Hillary Clinton: That is an outright lie
Bill Clinton CBS Sunay Morning
PHOTO: cbs
Bill Clinton CBS Sunay Morning
Now playing
01:32
Bill Clinton reflects on Trump media coverage
President Donald Trump speaks at a rally at the Gaylord Opryland Resort and Convention Center, Tuesday, May 29, 2018, in Nashville, Tenn. (AP Photo/Andrew Harnik)
PHOTO: Andrew Harnik/AP
President Donald Trump speaks at a rally at the Gaylord Opryland Resort and Convention Center, Tuesday, May 29, 2018, in Nashville, Tenn. (AP Photo/Andrew Harnik)
Now playing
01:06
Trump: I drew in bigger crowds than Jay-Z
PHOTO: Getty Images
Now playing
01:34
Chelsea Clinton slams Ivanka over Trump support
PHOTO: CNNI
Now playing
01:39
Hillary Clinton trolls Trump with Russian hat
AUSTIN, TX - NOVEMBER 17:  Former U.S. Secretary of State Hillary Rodham Clinton signs copies of her new book 'What Happened' at BookPeople on November 17, 2017 in Austin, Texas.  (Photo by Rick Kern/WireImage)
PHOTO: Rick Kern/WireImage/WireImage
AUSTIN, TX - NOVEMBER 17: Former U.S. Secretary of State Hillary Rodham Clinton signs copies of her new book 'What Happened' at BookPeople on November 17, 2017 in Austin, Texas. (Photo by Rick Kern/WireImage)
Now playing
01:29
Clinton: Trump parrots what Putin says
US Democratic presidential candidate Hillary Clinton makes a concession speech after being defeated by Republican President-elect Donald Trump, as former President Bill Clinton looks on in New York on November 9, 2016. / AFP / JEWEL SAMAD        (Photo credit should read JEWEL SAMAD/AFP/Getty Images)
PHOTO: JEWEL SAMAD/AFP/Getty Images
US Democratic presidential candidate Hillary Clinton makes a concession speech after being defeated by Republican President-elect Donald Trump, as former President Bill Clinton looks on in New York on November 9, 2016. / AFP / JEWEL SAMAD (Photo credit should read JEWEL SAMAD/AFP/Getty Images)
Now playing
02:01
Clinton: What went right, wrong in 2016
ST LOUIS, MO - OCTOBER 09:  Democratic presidential nominee former Secretary of State Hillary Clinton (R) speaks as Republican presidential nominee Donald Trump looks on during the town hall debate at Washington University on October 9, 2016 in St Louis, Missouri. This is the second of three presidential debates scheduled prior to the November 8th election.  (Photo by Rick Wilking-Pool/Getty Images)
PHOTO: Pool/Getty Images
ST LOUIS, MO - OCTOBER 09: Democratic presidential nominee former Secretary of State Hillary Clinton (R) speaks as Republican presidential nominee Donald Trump looks on during the town hall debate at Washington University on October 9, 2016 in St Louis, Missouri. This is the second of three presidential debates scheduled prior to the November 8th election. (Photo by Rick Wilking-Pool/Getty Images)
Now playing
02:07
Clinton: I was thinking 'back up, you creep'
Podesta talks Trump and Clinton_00055625.jpg
Podesta talks Trump and Clinton_00055625.jpg
Now playing
07:09
Podesta: Clinton is under Trump's skin
PHOTO: Comedy Central
Now playing
01:05
Trevor Noah on the benefit of Trump's tweets
PHOTO: Drew Angerer/Chip Somodevilla/Getty Images
Now playing
02:59
Clinton and Trump aides clash
Republican presidential candidate Donald Trump speaks before introducing his newly selected vice presidential running mate Mike Pence, governor of Indiana, during an event at the Hilton Midtown Hotel, July 16, 2016 in New York City.
PHOTO: Drew Angerer/Getty Images
Republican presidential candidate Donald Trump speaks before introducing his newly selected vice presidential running mate Mike Pence, governor of Indiana, during an event at the Hilton Midtown Hotel, July 16, 2016 in New York City.
Now playing
02:52
Push back on Trump's voter fraud allegations
MANCHESTER, NH - APRIL 12: Donald Trump speaks at the Freedom Summit at The Executive Court Banquet Facility April 12, 2014 in Manchester, New Hampshire. The Freedom Summit held its inaugural event where national conservative leaders bring together grassroots activists on the eve of tax day. Photo by Darren McCollester/Getty Images)
PHOTO: Darren McCollester/Getty Images/FILE
MANCHESTER, NH - APRIL 12: Donald Trump speaks at the Freedom Summit at The Executive Court Banquet Facility April 12, 2014 in Manchester, New Hampshire. The Freedom Summit held its inaugural event where national conservative leaders bring together grassroots activists on the eve of tax day. Photo by Darren McCollester/Getty Images)
Now playing
01:38
Trump tweets slam Clinton over recount
US Democratic presidential candidate Hillary Clinton (R) and US Republican presidential candidate Donald Trump shake hands at the end of the second presidential debate at Washington University in St. Louis, Missouri, on October 9, 2016. / AFP / Robyn Beck        (Photo credit should read ROBYN BECK/AFP/Getty Images)
PHOTO: ROBYN BECK/AFP/Getty Images
US Democratic presidential candidate Hillary Clinton (R) and US Republican presidential candidate Donald Trump shake hands at the end of the second presidential debate at Washington University in St. Louis, Missouri, on October 9, 2016. / AFP / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
Now playing
06:14
Duffy: I'm with Trump - don't go after Clinton

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.

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.

RELATED: Clinton, Trump battle for Pennsylvania

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.’”

Road to 270: CNN’s new electoral college map

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.”