In the heated discussions over the effects of fake news on democracy and civil society, Donald J. Trump has often taken center stage.
He has used false claims to attack his political opponents, question the legitimacy and loyalty of the Obama administration and other Democrats, and undermine the news media, the federal government and other institutions that many of his supporters do not trust.
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The practice has paralleled his rise from reality TV star to holder of the nation's highest elected office, according to an analysis of his social media activity.
When discussing some of his claims, Mr. Trump has cited as evidence articles posted through Breitbart News, manipulated YouTube videos and celebrity gossip publications like The National Enquirer.
Mr. Trump has also tweeted links from right-wing blogs like WND.com and TheRightScoop.com that often promote sensational conspiracy theories and contain little original reporting.
His sourcing highlights the bounty of misinformation accessible on the web and its power in a deeply divided America — especially when endorsed by someone of Mr. Trump's influence and visibility.
He offered this explanation for his actions while discussing an altered YouTube video he had tweeted as part of an unsubstantiated claim that a protester at one of his rallies had ties to the Islamic State: "I don't know what they made up; all I can do is play what's there," Mr. Trump said on NBC's "Meet the Press."
"All I know is what's on the internet."
Below are examples from the last several years of Mr. Trump's penchant for making fraudulent claims and backing them up with information gleaned from unsubstantiated sources.
In November 2011, Mr. Trump proclaimed that the Affordable Care Act would "ration care," linking to an article on TheRightScoop.com. The story cited an anonymous caller's comments on a conservative radio talk show as proof the act established so-called death panels that would determine whether or not elderly patients received care.
The notion of death panels was deemed the "Lie of the Year" in 2009 by the fact-checking website Politifact, which traced its rise to comments made by Sarah Palin on Facebook. The additional claims in the story Mr. Trump shared were debunked by the American Association of Neurological Surgeons and the Department of Health and Human Services, according to Snopes, another fact-checking website.
Mr. Trump took to Twitter to share a story from TheGatewayPundit.com, a conservative blog, which falsely claimed that Mr. Obama had issued a statement for "the fake holiday" Kwanzaa but not for Christmas. (Mr. Obama's Christian faith has been questioned by political opponents; some have sought to assail the legitimacy of his presidency by falsely claiming he is a Muslim.) After the political blog Talking Points Memo refuted the story, Mr. Trump shared it again on Twitter, starting his post with "I'm right, TPM is wrong."
President Obama and his wife wished Americans a "merry Christmas" on Dec. 24, 2011, in a video address shared on Twitter, YouTube and the White House website. Earlier that month, Mr. Obama said he hoped Americans had "the merriest of Christmases," as his family lit the National Christmas Tree in front of the White House, and separately said that "the story of Jesus Christ changed the world" in remarks at the "Christmas in Washington" concert. The statement on Kwanzaa was in line with those made by George W. Bush through 2008.
In March 2011, Mr. Trump started raising questions about President Obama's birthplace and birth certificate on television, on shows that included ABC's "The View" and NBC's "Today." The notion had been debunked and pushed to the realm of conspiracy theorists after Mr. Obama released his short-form birth certificate from the Hawaii Department of Health in 2008.
Mr. Trump also promoted his claims through Twitter, citing "an 'extremely credible source'" that called his office and allegedly told him the certificate was a fraud, as well as linking to posts on blogs like WND.com and FreedomOutpost.com. While Mr. Trump was roundly denounced for continuing to push the conspiracy theory, it solidified his connection to the largely white Republican base that was so instrumental in his election victory in November.
Mr. Trump has also made claims without supporting material of any kind. He once shared political views through a YouTube video series, "From The Desk Of Donald Trump," sounding off on the Republican Party and Mr. Obama, but also on topics as varied as Andy Roddick's talent and the state of the desk itself. ("Many people have been asking about my desk and the fact that I have so many papers on my desk," it began.) He tweeted links to the posts with the hashtag #trumpvlog throughout 2011 and 2012.
In April 2012, Mr. Trump posted a segment in which he said, "I have no doubt in my mind that President Obama made a deal with the Saudis to flood the markets with oil before the election so he can at least keep it down a little bit."
He added: "After the election it's going to be a mess. You're going to see numbers like you've never seen if he wins." He repeated this allegation about a secret deal on CNBC in June of that year, which Fox published under the headline "Trump: Obama's Secret Saudi Oil Deal to Win Re-election."
Starting in 2012, Mr. Trump has repeatedly expressed his personal belief that autism is linked to childhood vaccinations, saying it in interviews, on Twitter, and even during a Republican debate.
On the show "Fox & Friends" in April 2012, Mr. Trump was asked about the rising number of children with autism diagnoses and said, "I have a theory and it's a theory that some people believe in, and that's the vaccinations." Later in the segment, one host noted most doctors disagree and that studies do not show a link, which Mr. Trump acknowledged, adding, "It's also very controversial to even say, but I couldn't care less." He said he had seen changes in children firsthand to support his belief.
Plenty of studies, including a recent one that involved almost 100,000 children, have shown there is no scientific evidence linking vaccinations to autism, and that there is no benefit to delaying vaccinations. Instead, children who are not vaccinated on the regular schedule can be at risk for infectious diseases for a longer period. One doctor told Scientific American that "misinformation on the internet often frightens parents away from following" the vaccination schedule recommended by the Centers for Disease Control and Prevention, the only one endorsed by the American Academy of Pediatrics. In 2015, a measles outbreak in California, which started at Disneyland, was partly attributed to diseases spread by children who were not vaccinated.
In October 2012, Mr. Trump took to Twitter to ask why President Obama's administration was not intervening. He then wrote in March 2014, "If I were President I would push for proper vaccinations but would not allow one time massive shots that a small child cannot take - AUTISM."
Mr. Trump has a long history of casting doubt on the unemployment data and figures on "underemployment," a measure that also includes people working part time for lack of full-time jobs and others who have given up looking for work. In mid-2012, he remarked on Twitter that an underemployment rate of 14.9 percent was "way low," and could actually be 20 percent. A couple of months after that, he said on CNBC that "the real unemployment number is over 17 percent, when you add back the tremendous numbers of people that gave up looking for jobs and all of the other things they do to manipulate them."
In November 2013, Mr. Trump, on Twitter, linked to a column from The New York Post headlined, "Census 'faked' 2012 election jobs report." The story was quickly criticized by The Columbia Journalism Review for "turning a nugget of news into a blockbuster conspiracy exposé." It noted that the column was largely premised on the misbehavior of a worker who left the Census Bureau in 2011, well before the election.
In December 2014, Mr. Trump tweeted a story from WND.com, a conspiracy-minded conservative site, with the headline "Donald Trump: Obama's Jobless Figures 'Phony.' Economists agree." The story cited comments Mr. Trump made on "Fox & Friends" alleging that the actual unemployment rate was almost 18 percent, an estimate supported by John Williams, an independent economist who has a newsletter called "Shadow Government Statistics." It says says it "exposes and analyzes flaws in current U.S. government economic data and reporting."
Mr. Williams, in the WND story, estimated November unemployment at 23 percent. Trump later repeated that figure during a campaign speech at Liberty University in January 2016, a number The Washington Post showed to be false.
Mr. Trump shared a link from TheRightScoop.com on Twitter, claiming the president's budget "cut domestic bomb prevention in half." The post relied on a story from The Daily Mail, which based its claim on an estimate from a former official at the Department of Homeland Security who resigned in 2005.
Separately, Mr. Trump tweeted, "Is the Boston killer eligible for Obama Care to bring him back to health?" He went on to circulate a post based entirely on that tweet from Newsbusters.org, a blog from the Media Research Center, which states its goal as "documenting, exposing and neutralizing liberal media bias." Outside of the fact that federal law requires any patient requiring emergency treatment to be treated regardless of insurance status or ability to pay, the attack occurred in Massachusetts, where the health insurance program under Mitt Romney served as a model for the Affordable Care Act.
Mr. Trump made comments in a Fox News interview last May accusing Senator Ted Cruz's father of associating with Lee Harvey Oswald shortly before the assassination of President John F. Kennedy.
Mr. Trump's remarks — made on the day of the Republican primary in Indiana — came after The National Enquirer claimed it had photographic proof that Mr. Cruz's father, Rafael Cruz, was "palling around" with Mr. Oswald before the shooting. Mr. Cruz's campaign called that report error-filled and condemned Mr. Trump for campaigning "on false tabloid garbage."
The fact-checking website Politifact noted that "several historians of the period told us they've never seen Cruz's name come up in connection with Oswald."
Mr. Trump claimed at a rally last year that a man who charged him at another event was linked to the Islamic State, yet no government agency suggested the man was connected to ISIS or terrorism. He repeated the allegation in a tweet, linking to a video that claimed to show the man. It was overlaid with Arabic text and music and appeared to have been created as a hoax.
When asked on NBC's "Meet the Press" about the lack of evidence tying the man to ISIS and the video hoax, Mr. Trump did not seem deterred.
"He was dragging a flag along the ground and he was playing a certain type of music and supposedly there was chatter about ISIS," he responded. "What do I know about it?"
After winning the presidential election but losing the popular vote, Mr. Trump took to Twitter to claim that he actually received more votes than Mrs. Clinton "if you deduct the millions of people who voted illegally." The notion was popularized by Infowars, a website replete with conspiracy theories that include questioning the shooting at Sandy Hook Elementary School.
The overwhelming consensus from people who oversaw the general election in states around the country was that the amount of voter fraud in 2016 was next to none.