Monica Crowley at Trump Tower in New York on Dec. 15. (Pool photo by Albin Lohr-Jones via European Pressphoto Agency)

In the early hours of July 10, D.C. resident Seth Rich was fatally shot near his home.

Police said the 27-year-old Democratic staffer was probably the victim of an attempted robbery. But Monica Crowley, a Fox News analyst who recently joined President-elect Donald Trump’s national security team, suggested a different culprit: Hillary Clinton.

“Maybe, in fact, it wasn’t a robbery,” Crowley said Aug. 10 on “The O’Reilly Factor.” “Maybe there was something more sinister here. . . . The question going forward, I think for Mrs. Clinton, for everybody here, is what else is out there? Who has it? Whose life may be in danger?”

Those comments are typical of the perspective Crowley brings to her appointment as senior director for strategic communications for the National Security Council. But it’s not just her. Many of Trump’s highest-level appointees have a history of publicly promoting conspiratorial, outlandish and fringe beliefs, particularly about Muslims, the Clinton family and the environment — unproven narratives that remain stubbornly alive on the Internet despite being debunked by the mainstream media.

Those who promote such narratives include top Trump national security staffers, advisers and Cabinet designees, many of whom will enter the executive branch with long records of public statements from their careers as conservative commentators and politicians. Their open and shared tendency toward repeating false narratives, a more prevalent theme in this administration than previous ones, raises questions about what role debunked and discredited theories might play in Trump’s decisions as president.

(Peter Stevenson/The Washington Post)

The question is particularly urgent given Trump’s own pattern of conspiratorial statements — he rose to political prominence after repeatedly raising the false idea that President Obama was not born in the United States — and his refusal to accept a daily briefing from the intelligence community. He has said he prefers to rely on updates from his advisers, some of whom have promulgated such false narratives.

Trump’s transition team did not respond to a request to comment for this article.

Mark Fenster, author of “Conspiracy Theories: Secrecy and Power in American Culture,” said touting such unproven narratives can bias the judgment of people in power, with real consequences.

“You might inaccurately or unfairly interpret information that comes your way. You might seek out a limited number of sources of information and make decisions that are not as good as they could otherwise have been,” said Fenster, a professor at the University of Florida’s Levin College of Law. “The federal government is facing very complex issues on a regular basis that require political judgment calls. . . . If someone has certain cognitive predispositions, it can lead to wrong answers.”

Less than 30 days from Trump’s inauguration, for example, his designee to lead the Office of Management and Budget, Rep. Mick Mulvaney (R-S.C.), is being scrutinized for his choice in July to speak to a chapter of the John Birch Society, a far-right group known for its paranoia about the Federal Reserve and the possibility of world government. The group was once estranged from mainstream conservatism because of its conspiratorial views, but that did not stop Mulvaney from praising and encouraging its work, according to Mother Jones, citing audio of the speech.

Controversial beliefs, often nurtured and grown in a petri dish of partisan websites before becoming more widely known, are starting to have real-world consequences.

On Dec. 4, a North Carolina man entered a D.C. pizza parlor armed with an AR-15 rifle, bent on investigating rumors about a child sex ring with purported ties to Clinton that he believed operated in tunnels beneath the restaurant.

(Erin Patrick O'Connor,Manuel Roig-Franzia/The Washington Post)

The man, 28-year-old Edgar Welch, was arrested and now faces the possibility of 30 years in prison. He found nothing.

“It would be unfair and inaccurate to say that conspiracy theories lead to violent acts necessarily, but at a time of heightened political drama, they can,” Fenster said.

“Pizzagate” gained steam on Twitter after user @DavidGoldbergNY claimed on Oct. 30 that Clinton-related emails newly discovered by the FBI “point to a pedophilia ring” with Clinton “at the center.” The theory traveled to Reddit and 4chan before finding a proponent in Alex Jones, the far-right radio talk-show host on whose show Trump and his acolyte Roger Stone, who often promotes such conspiracies, have appeared. Soon, the theory incorporated the fact that Clinton campaign chairman John Podesta had dined at the D.C. pizzeria Comet Ping Pong. The hashtag #pizzagate was born and quickly spread with the help of unmanned programs known as bots.

Members of Trump’s inner circle have stoked similarly lurid rumors about the Clintons. On Nov. 3, retired Lt. Gen. Michael Flynn, now Trump’s pick for national security adviser, tweeted a link to an online post claiming the New York Police Department had evidence linking Clinton to “child exploitation” and “sex crimes with minors.” “U decide,” Flynn wrote, calling the post a “must-read.” He has since deleted the tweet.

Online media amplifies such theories, helping them gain traffic in remote and niche corners of the Internet. Conservative websites such as Breitbart, the Drudge Report, Infowars and WND play host to the least-scrupulous theorizing. Sometimes, their coverage drives discussion at more prominent outlets such as Fox News. Social media produces memes that get picked up by public figures, including lawmakers. Eventually, mainstream media outlets may carry the rumors, if only to debunk them.

Joseph Uscinski, an associate professor at the University of Miami, said the risk of having conspiracists in government is they can act on those beliefs “with the force of law.”

“In other institutional contexts, we’ve seen the damage that conspiracy theorists can do when they have power,” said Uscinski, co-author of “American Conspiracy Theories,” published in 2014. “Hitler and Stalin come to mind, though those were very different institutional contexts.”

At the same time, Uscinski said, survey data shows that everyone believes in at least one conspiracy theory. “It is not shocking to hear that people in government believe a few,” he said. “What it comes down to is which ones do they believe and whether they are actionable.”

These views go far beyond the consensus among many in Trump’s world that climate change is a hoax perpetrated by scientists or that voter fraud does, contrary to the evidence, take place on a vast scale.

Accusations of anti-Semitism have been leveled at Stephen K. Bannon, Trump’s senior adviser and the former head of Breitbart News, which has run columns with strong conspiratorial, anti-Semitic overtones. Bannon’s ex-wife said in a sworn court declaration in 2007 that Bannon has said he doesn’t like Jews and doesn’t want his children to attend school with them. Bannon, through a spokeswoman, has denied making these statements.

Trump, too, has been accused of fueling anti-Semitism with some of his rhetoric and campaign imagery. His final ad used photos of prominent Jews to illustrate “those who control the levers of power” and a “global power structure,” drawing a rebuke from the Anti-Defamation League.

Still, few of Trump’s advisers publicly espouse anti-Semitic views. The unproven narratives they promote are more likely to center on Islam.

Bannon, along with many others in the conservative media, has promoted the narrative that Clinton’s closest aide, Huma Abedin, is a tool of the Muslim Brotherhood.

Crowley, in 2008, called Obama “Arab African” and accused him of lying about his heritage, echoing Trump’s long history of claims that Obama was not born in the United States, retracted late in the campaign under pressure from critics. Trump has also falsely suggested that Obama is Muslim.

Flynn frequently warns audiences, without merit, that Islamic law is taking root in the United States. One of his claims, which has been repeatedly batted down by fact-checkers, is that Democratic state senators voted to impose it in Florida.

“Our country was built upon the foundation of Judeo-Christian principles, values, norms,” Flynn told an audience on Aug. 23. “We should fight this idea of this imposition of sharia law into our system. And believe me, folks, it is happening.”

Flynn later called “Islamism” a “vicious cancer” that “has to be excised,” comparing it to Nazism and fascism.

Clinton is a target of more than her fair share of unfounded allegations.

Kathleen “KT” McFarland, Trump’s pick to be Flynn’s deputy, claimed in 2006 that Clinton dispatched helicopters to surveil her house as she campaigned for Senate. McFarland has also argued that Clinton and other members of the Obama administration “traded lives for votes” in their handling of the 2012 terrorist attacks in Benghazi, Libya.

Crowley was among the original conservative commentators accusing Clinton of false illnesses, suggesting in December 2012 she had faked a reported concussion to avoid testifying before the House about the Benghazi attacks. Clinton’s testimony was postponed until Jan. 23, 2013.

Few have gone further than Rep. Ryan Zinke (R-Mont.), Trump’s pick for interior secretary, who told voters in 2014 that Clinton was “the real enemy” — “the Antichrist.”

Other Trump appointees are known for airing strange and unproven theories. Former Texas governor Rick Perry, who Trump will nominate for energy secretary, in 2014 repeatedly claimed without evidence that Obama was responsible for a surge in undocumented immigrants crossing the Texas border.

“We either have an incredibly inept administration or they’re in on this somehow or another,” Perry told ABC News in July 2014. “I mean, I hate to be conspiratorial, but I mean, how do you move that many people from Central America across Mexico and then into the United States without there being a fairly coordinated effort?”

Retired surgeon Ben Carson, who will lead the Department of Housing and Urban Development if he’s confirmed, exists in what occasionally seems like his own universe of theories, claiming at times that prison makes inmates gay, that the devil is responsible for the theory of evolution and that the pyramids were originally constructed not as tombs but to store grain.

Carson, Perry and Trump have all suggested that the Obama administration manipulates its monthly unemployment rate to paint a rosier picture of economic growth, a conspiracy dubbed unemployment “trutherism.” Former General Electric chief executive Jack Welch, a member of Trump’s kitchen cabinet of corporate leaders, also has espoused this view.