Paul Musgrave is an assistant professor at the University of Massachusetts Amherst.
Here's what happened after President Trump fired off a tweet accusing former president Barack Obama of wiretapping Trump Tower before the 2016 election. (Monica Akhtar/The Washington Post)

This past weekend, President Trump accused former president Barack Obama — without any evidence — of ordering Trump’s phones to be wiretapped during last year’s presidential campaign. It was only the most recent in a bewildering number of conspiracy theories the president and his circle have embraced over the past year. In 2017, having the president of the United States openly disregard the truth for short-term political gain is the new normal. And that is not normal.

This is a dangerous time for democracy. Less than two months into the administration, the danger is no longer that Trump will make conspiracy thinking mainstream. That has already come to pass. Conspiracy theories, rumor and outright lies now drive the news cycle, as the weekend demonstrated once again. (Earlier examples included Trump’s false claim about widespread voter fraud and his misrepresentations about a Navy SEAL raid in Yemen.) Far worse, such untruths may now be driving government policy in realms as disparate as immigration policy and civil rights. In the long term, the damage done to trust by the normalization of untruth may threaten the social contract on which democracy itself rests.

Hostility toward facts is at the core of Trump’s governing style. Trump and his advisers do not innocently repeat conspiracy theories about the subjects they choose, whether it’s largely imaginary voter fraud or the false claim that Sen. Ted Cruz’s father was involved in the assassination of President John F. Kennedy. By now, it’s hard not to be suspicious that a pattern of repeatedly bringing up untruths and rumors is more than a coincidence. Judged strictly on results, Trump’s methods have proven incredibly effective. As University of Miami political scientist Joe Uscinski pointed out last year, if anything, voters rewarded Trump for running a campaign that rejected facts.

How did conspiracy theories come to pose such a challenge to truth? The long-term decline in general trust played a crucial role. As political scientists Joanne Miller, Kyle Saunders and Christina Farhart observe, to believe in a successful conspiracy, one must first believe that powerful actors are willing to conspire against the public — hardly the position of someone who believes that elites make the best, or at least good, choices. As more people came to mistrust authority, they became susceptible to stories about how good people like them were being betrayed by nefarious elites.

Growing political polarization provided the second necessary ingredient. As voters have become more and more likely to identify with strongly and vote for their preferred political party, they have also become more closed off from other viewpoints. The creation of partisan echo chambers on social media and in other institutions has accelerated the growth of conspiracy thinking. As Norbert Schwarz, Eryn Newman and William Leach note in “Behavioral Science and Policy,” people judge whether they should believe an argument not through rigorous fact-checking but through criteria, such as coherence, familiarity and plausibility.

Polarization generates closed loops in which believing untruths about the “other side” becomes more plausible than seeking out information that might challenge those ideas, as The Washington Post’s Ishaan Tharoor suggested Monday. Thus, conspiracy theories can come to seem more plausible than objective sources, even if only just through repetition. Similarly, Schwarz, Newman and Leach suggest that brains judge coherence by whether a claim tells a good story. Ironically, that means that unfalsifiable conspiracy theories, in which everything can be explained as evidence of a sinister design, lends them a coherence that reality, full of coincidence and randomness, can never have.

To be fair, Trump did not create the conditions for the rise of untruth. Through luck or design, however, he has exploited it. Moreover, his embrace of fringe thinking has led to a reversal of a usual pattern. Before 2017, conspiracy thinking was a feature of the party out of power. Now, however, Republicans have continued to embrace ideas like “DeepStateGate” even though they control almost the entire edifice of government, from the White House and Capitol to two-thirds of state legislatures.

The damage to the foundations of a fact-based discourse has seeped to both sides. Last week, liberals and Democrats crowed about Attorney General Jeff Sessions’s admission that he had met with Russian Ambassador Sergey Kislyak during the 2016 campaign. The subtext — and sometimes text — was that Sessions may have helped coordinate a Kremlin-based plot to steal the election. The evidence supports no such assertion; as Ryan Lizza wrote in the New Yorker, so far this appears to be a “cover-up without a crime.” Yet the echo chambers of Twitter resounded with liberals eagerly sharing the news and hoping that Sessions would resign for a highly visible — but still undefined — transgression.

In the longer term, the feedback loop of lies begetting rumor will threaten the foundation of democracy. Democracy requires trust — including the fundamental trust that losing an election does not mean losing power forever. Not only do conspiracy theories feed on mistrust of authority, they also promote mistrust. If a substantial fraction of Americans believes that their political opponents have become their enemies, then the basis for compromise and accommodation that democratic institutions produce will collapse. Through his actions, Trump is bidding for that to be his most lasting legacy.