“When will it sink in that MAGA was an Op and Trump is a spy?” asks Emmy award-winning investigative reporter Heidi Cuda after the Federal Bureau of Information search of Mar-a-Lago. 

Her comment underscores the extent to which conspiracy theories prevail on both the left and right sides of the political spectrum. The unbounded distrust of authorities at the heart of any conspiracy mindset has long had a home on the far left.

Opinion data show an equal number of Americans on the left and the right share the belief that a secret cabal controls events and rules the world. 

From this central belief emerge the varying theories and related obsessions, whose appeal breaks down along partisan lines: The Obamas and the Clintons as the evildoers on one side, President Trump on the other; George Soros as fodder for the right, the Koch brothers for the left.

The reaction to the FBI raid shows how the “Orange Man” remains central to left-wing conspiracy narratives.  These theories include the belief that Mr. Trump faked Covid, as filmmaker Michael Moore asserted. The former senior advisor to President Obama, David Axelrod, likewise posited on CNN, “Did Trump try to cover up his Covid-19 infection?” 

Then there is the claim that Mr. Trump had a body double of his wife accompany him on work trips, which the Trump White House even felt compelled to refute in an official statement. The body double theory has aired on mainstream shows and outlets, such as ABC’s The View — where host Joy Behar claimed, “I don’t think that’s her nose.”

Of course, the most pervasive and potent conspiracy theory is that Mr. Trump is collaborating with hostile foreign powers to damage the United States. Following the FBI raid, #TrumpTreason trended on Twitter. 

After news broke that the FBI had taken Mr. Trump’s passports, a Democratic congressman, Ted Lieu, tweeted “Maybe one of the passports is Russian.” 

This dual-loyalty charge is hardly new. As Speaker Pelosi claimed two years ago, “With him, all roads lead to Putin.” 

Democratic Representative Eric Swalwell is free of doubts: Trump “would ABSOLUTELY trade America’s deepest secrets to benefit himself.” On MSNBC, meanwhile, suspicions turned to Saudi Arabia. Political commentator Mike Barnicle couldn’t “help but think” that Mr. Trump “would look at a document” and “wonder how much they’d pay to know this in Riyadh?”  

Just a few days after the raid Tiffany Cross on MSNBC asked her guest what the punishment for Trump would be, “given that this could really be a situation where you’re a traitor, actually a traitor to America, if it’s confirmed that he was actually trafficking information about nuclear weapons?” 

On the right, Mr. Trump himself is the chief proponent of claims that the 2020 elections were rigged. On the left, top leaders have sometimes aired comparable suspicions about Mr. Trump’s victory in 2016.

“There certainly was an understanding of some sort” between Trump and the Russians, claimed Secretary Clinton in 2017. President Carter said that Mr. Trump “lost the election and he was put into office because the Russians interfered.”

“Wholly in the pocket of Putin” is how the former CIA director, John Brennan, described Mr. Trump.

Media figures promoted a similar narrative. The book “American Kompromat,” a sordid tale of how the KGB groomed Mr. Trump for more than 40 years, was a New York Times instant bestseller: “A must-read. The gun’s not quite smoking, but the barrel’s plenty hot, and there are Russian shell casings all around,” read one review. 

Mainstream outlets promoted the book’s allegations with headlines suited to spy thriller movies. Examples include “Trump Kompromat Claimed: Kremlin Documents Reportedly Show Putin Conspiring For Billionaire” from Forbes, or “Will Trump Be Meeting With His Counterpart — Or His Handler?” from New York Magazine.

Even earlier, there were signs of Americans’ readiness to believe the worst about elections, especially claims that the 2004 presidential election was stolen from Senator Kerry through the manipulation of voting machines. 

Conspiracy theorist Mark Crispin Miller dedicated a book to proving the election was stolen, and such notables as Senator Daschle and Barbra Streisand endorsed it. Mrs. Pelosi, Senator Reid, and Governor Dean of Vermont mourned the fall of electoral integrity and voiced concerns about ballot tampering in the re-election of President George W. Bush. 

Theresa Heinz Kerry blamed her husband’s electoral loss on “rigged voting machines” owned by “hard right” Republicans. There may not have been a “Stop the Steal” movement in 2004, but the idea of a “steal” was prevalent in left-wing circles.

Regrettably, leaders with a disregard for the truth are finding voters ready to believe them. Many Republicans still believe that Mr. Trump is the “legitimate president.” A majority of Democrats believed that Russia tampered with vote tallies to get Mr. Trump elected (never mind that a Senate report found no Russian interference in the actual vote count).

The response to the FBI raid shows yet again how conspiracy theories are no longer exclusive to fringe elements on the right.