In an almost entirely unprecedented moment, Donald Trump, the presumptive Republican nominee for president, suggested in interviews Monday morning that President Obama may have somehow been involved in Sunday’s massacre in Orlando.

Trump’s suggestion came by implication, but the message is unmistakable: The president may have somehow known about or been involved in the shooting.

“He doesn’t get it or he gets it better than anybody understands—it’s one or the other and either one is unacceptable,” Trump said on Fox News. He had already called in a statement Sunday for Obama to resign from office. Trump added on Monday:

Look, we’re led by a man that either is not tough, not smart, or he’s got something else in mind. And the something else in mind—you know, people can’t believe it. People cannot, they cannot believe that President Obama is acting the way he acts and can’t even mention the words “radical Islamic terrorism.” There’s something going on. It’s inconceivable. There’s something going on.

During an interview on NBC’s Today show, Trump offered a slightly softer version of the accusation, suggesting Obama was willfully blind: “There are a lot of people that think maybe he doesn’t want to get it.”

The idea the president is a Manchurian candidate, a mole or agent for jihadism is a stunning accusation, even by the standard of a presidential campaign in which Trump has delivered a series of breathtaking statements, from comparing a rival to a child molester to being unable and unwilling to differentiate one of his policy ideas from Nazi policies.

Such conspiratorial beliefs are not unheard of in American politics, but they are typically banished to the margins. For example, some “Truthers” argued that President George W. Bush was either involved in or turned a blind eye to the 9/11 attacks. There’s no substantiation for those claims, and the people who hold them are generally viewed with derision. So, too, are those who have claimed that mass-shooting events such as the Sandy Hook massacre are “false flag” attacks, designed to drum up support for gun-control measures. The fringe radio host Alex Jones has already labeled Orlando a false flag, offering a sense of who Trump’s allies are on this issue.

What is unprecedented here is that the claims are coming from a major party’s presumptive nominee for president, but unhinged beliefs about Obama are not especially new, nor are they nearly so fringe. The conservative writer Andrew McCarthy argued in a 2010 book that Obama was part of a conspiracy with radical Islamists to subvert the U.S. government. More banally, many people have claimed that Obama is a Manchurian candidate (or a Manchurian president, perhaps), a non-U.S. citizen who is ineligible for the presidency. That claim, too, is bogus, contradicted by a raft of evidence, including Obama’s birth certificate and contemporaneous birth announcements in Hawaii newspapers. Nonetheless, polls as recently as this year have found a majority of Republicans questioning Obama’s citizenship.

These “Birthers” have been encouraged by supporters in upper echelons of politics. In 2011, for example, a prominent businessman began voicing doubts about Obama’s citizenship. He even said he had bankrolled investigators, sending them to Hawaii to look into the matter. (Whether he really did is unclear.) He even claimed that they’d turned up incriminating information. In the end, of course, no such evidence turned up, although the pressure did apparently convince Obama to release his “long-form” birth certificate, a white whale for birthers. Despite what might have been a discrediting experience for the businessman in the eyes of the public, he didn’t slink away and stay quiet. Instead, he ran for president in 2016, and he’s now the GOP nominee: Donald Trump.