Donald Trump has made misinformation into a campaign tactic. (Mary Schwalm/Reuters)

Trump has embraced some of the ideas by radio host and conspiracy theorist Alex Jones. (Oli Scarff/Getty Images)

Alex Jones may be America’s most successful conspiracy theorist. On his website, Infowars.com, and his daily radio program heard on more than 100 stations nationwide, Jones regularly promotes a variety of ­beyond-the- fringe ideas: alleged government conspiracies in the Oklahoma City bombing in 1995 and the terrorist attacks of Sept. 11, 2001; fluoride-in-the-water health scares; suspicions that the moon landings were faked; doubts about President Obama’s place of birth and birth certificate.

Jones, in short, may be Donald Trump’s kind of guy.

The ranting radio host and the leading Republican candidate shared a microphone, and some common ground, last week in what may have been a dubious first — the first time a leading presidential candidate has been interviewed by a media figure from the far extremes. “Your reputation is amazing,” Trump assured Jones, after Jones assured Trump that most of his listeners supported his candidacy. “I will not let you down.”

Trump finding common ground with Jones is in keeping with Trump’s own rocky relationship with facts and credible information during the campaign. Many of Trump’s more controversial assertions since he declared for president have come from the murky swamp of right-wing, libertarian and flat-out paranoid sources that have proliferated and thrived as the Internet and social media have grown.

Once a small fringe, this “alternative” information ecosystem now includes websites, talk-radio programs, newsletters, conferences and “citizen journalists” who promote, debate and inflate such questionable causes as vaccine denial, climate-change skepticism , and the supposedly imminent imposition of sharia law in America. The fringe nowadays often injects its ideas into the mainstream by gaining the attention of sources broadly popular among conservatives, such as Fox News and the Drudge Report, which devoted attention to rumors that the Operation Jade Helm military exercises this summer in the Southwest were a prelude to a crackdown on civil liberties.

“There’s an information-age tsunami out there that just keeps getting bigger and bigger,” said Steve Smith, a veteran newspaper editor who teaches journalism at the University of Idaho. “When you combine this digital tsunami with the loss of quality and quantity in American journalism [due to cutbacks and economic woes] over the years . . . journalists just don’t have the ability to keep up once a false narrative gains speed.”

At the same time, Trump has been the most aggressive in the Republican field in denouncing the mainstream media, the erstwhile arbiter of fact. Many of his condemnations of mainstream reporters have been echoed by Trump’s army of Twitter followers and supportive websites, such as the conservative Breitbart.com.

Trump, in turn, cites his Twitter followers as the source for some of his own non-facts, such as his recent claim that ­African Americans killed 81 percent of white homicide victims (the actual number is closer to 15 percent, according to Factcheck.org). He defended his position of not allowing Muslims to enter the United States by citing a poll conducted by the Center for Security Policy, a think tank known for a variety of conspiracy theories, such as that members of the Muslim Brotherhood have infiltrated the Obama administration.

The result is a kind of self-reinforcing information loop in which Trump introduces some inaccurate statement, is called on it by the news media, which is then denounced by Trump for its supposed bias against him.

“It’s really jarring because he’s defying the rules of evidence that we have come to expect of people in leadership,” said Kathleen Hall Jamieson, a professor of communication at the University of Pennsylvania and the director of its Annenberg Public Policy Center. While not everything Trump says is true, Jamieson said Trump is “telling his supporters what they want to believe is true.”

Trump’s most famously false contention, of course, was his long, pre-campaign embrace of “birtherism,” the notion that Obama wasn’t born on American soil and is therefore ineligible to be president. Despite ample evidence to the contrary, including a birth certificate issued in Hawaii and a contemporaneous newspaper birth announcement, birther sites — from Birthers.org to Obamabirthbook.com — are strewn across the Internet, actively promoting a debunked thesis.

Accurate or not, the constant sowing of doubt has had a cumulative effect: Some 20 percent of people in a recent CNN/ORC poll said they believe Obama was born outside the country; 29 percent (and 43 percent of Republicans) said they believe Obama is a Muslim despite Obama’s profession of the Christian faith.

Trump isn’t the first politician with a tenuous grasp of the facts, of course. But he may be the first politician to exploit both widespread, bipartisan distrust of conventional news sources and the alternative reality provided by the digital grass roots, from sites such as Jones’s Infowars to chain emails to social media.

For example, Trump’s recent evidence-free assertion that “thousands” of Muslim Americans in New Jersey celebrated the fall of the World Trade Center towers on 9/11 parallels stories that have appeared in various forms in chain emails and elsewhere on the Web for years.

Trump never cited a source for his claim in November that Obama wants to take in as many as 250,000 Syrian refugees (Obama has proposed accepting 10,000 Syrians). But the fact-checking site Politifact traced the story to a website called Real News Right Now, which posts fake news stories, including one in September that said FEMA would resettle 250,000 Syrians in remote parts of Arizona and North Dakota.

The Internet has greatly facilitated the speed and reach of such misinformation, said Angie Drobnic Holan, Politifact’s editor. The Internet has also made it possible for people with like-minded, if bogus, ideas and theories to organize into communities and reach others, she said. “If you think the moon landing was fake, you can go on and find people just like you,” Holan said.

Social media has added another link to the misinformation chain, she noted. Erroneous information passed from peer to peer on Facebook or elsewhere often has an equal or even greater degree of credibility than a news report because people tend to trust those they know or are acquainted with compared with an anonymous media story, she said.

Trump’s misinformation may be “strategic,” said Jeffery Hemsley, an assistant professor in the school of information studies at Syracuse University. “Each candidate isn’t talking to the public as a whole — they are talking to their base and to those they might be able to persuade into voting for them,” he said. “So for many centrists and those on the left, Trump seems crazy. But for a segment of those on the right, Trump speaks to them. If Trump is using poor sources for his information, that isn’t really a problem for his audience. That is where they are getting their information, too.”

Hemsley, the co-author of “Going Viral,” about the rapid spread of information, said the days when the nation had “a somewhat unifying story” from newspapers and the leading TV news networks are gone. Nowadays, people tend to pick their own news, and like-minded social contacts, which tends to reinforce their beliefs rather than challenge them.

This makes it increasingly difficult to dislodge misinformation, he said. Good information can still drive out bad, but usually only when “the truth is sexier than the lie.”

“Facts may be undervalued or losing their value in today’s world,” said Robert Mason, a University of Washington professor who has researched the spread of false information. “If you say it loud enough or long enough, people will believe it. That’s okay in theory, but when people act on it, that’s a problem.”