As the House of Representatives canceled its session amid reported threats to the Capitol on Thursday, researchers who had warned of trouble ahead of the Jan. 6 siege found themselves scratching their heads. If something was brewing, they said, it was much smaller, quieter and less obviously violent than what they had reported two months ago — when they had struggled to get authorities to take their warnings seriously.

That contrast was even more startling as Thursday proceeded with few signs of trouble, and a sunny Washington eased into springlike bloom. The Capitol grounds remained quiet behind black metal fences guarded by heavily armed troops.

The apparent quiescence was matched online, where some pro-Trump forums that had fomented and celebrated the Jan. 6 attack dismissed the idea of a March 4 repeat as ridiculous confection — “fake news” or, worse, a trap to ensnare activists who so far have escaped arrest.

“No one is doing anything today,” said a prominent thread on Patriots.win, a successor to TheDonald.win, a site that played a central role in planning ahead of the Jan. 6 storming of the Capitol. “This is a lie the government created to make YOU the bad guy.”

Adherents of the baseless QAnon ideology had promoted the idea of a March 4 insurrection online several weeks ago — both before and after President Biden’s inauguration — as a supposed date for the return to power of former president Trump. That had been the nation’s inauguration date for most of its first century and a half before it was changed, by constitutional amendment, in the 1930s.

The idea of a looming threat had gained credence Wednesday when the Capitol Police, which along with other authorities had failed to prepare sufficiently for the thousands of Trump supporters who thronged the Capitol grounds on Jan. 6, warned that an unnamed militant group was planning to attack on Thursday. The House canceled proceedings in response to the Capitol Police warning, though the Senate remained in session.

But independent researchers did not share the alarm.

“I understand why Congress would want to be cautious, but whatever threat was presented by this conspiracy theory for March 4 wasn’t anywhere near the level for January 6,” said Rita Katz, executive director of SITE Intelligence Group, which had issued numerous reports before Jan. 6 detailing how a violent attack was being planned online, in plain sight. “Some from QAnon, militia groups and far-right circles have even advised against going to D.C.”

The Capitol Police did not immediately respond to a request for comment Thursday. The department’s statement Wednesday about a potential assault said it couldn’t release more details because of the “sensitive nature” of the intelligence and that it would be “prepared for any potential threats.”

The bogus claims of Trump’s “secret inauguration” on March 4 had helped rally some QAnon believers in the aftermath of Trump’s loss, researchers said. It allowed them to argue that they hadn’t been wrong, just early, when they’d argued for months that Trump would lead a climactic blitz to dismantle his enemies.

But with Trump in Florida, there was little to fan these predictions.

“Without Trump, there’s no leader here,” said Eric Feinberg, vice president for content moderation for the Coalition for a Safer Web, which monitors extremist content. “This thing, it’s a joke.”

The theory about Trump returning on March 4 never became a core part of the extremist QAnon ideology, and many believers online bickered over whether it was actually a hoax that would only serve to undermine the movement. Some prominent QAnon promoters began characterizing the idea as a “false flag” intended to draw fellow adherents into a trap.

“QAnon influencers used this conspiracy theory as a way to bring people together” after a series of losses, tweeted Marc-André Argentino, a research fellow at the International Center for the Study of Radicalization in London. “What they didn’t realize in all likelihood is the legs that this conspiracy theory would have.”

The disorder again underlined the risks for an online movement rooted in anonymity, researchers said: Few people were all that confident in what they could believe, trust or support. QAnon-boosting groups on the Telegram chat app have in recent days shared messages saying that anyone going to the Capitol on Thursday “IS A LEFTY TERRORIST.”

That confusion has been made worse by the disappearance of QAnon’s unnamed prophet, Q. The anonymous figure, who claimed to a have top-secret government clearance and intelligence on Trump’s covert ploys, has not posted online in 86 days.

Some QAnon believers have cited a Q post from 2019 to suggest that their mysterious leader had known the day was a setup all along, because the words “Mar 4" and “Trap” could be seen near each other in one of Q's more than 4,000 cryptic posts.

“Q HAS TOLD US MARCH 4 IS A TRAP (THEREFORE ANYTHING THAT HAPPENS IS NOT US!!)” said one post Thursday morning on a QAnon message board named for the “Great Awakening.”

Travis View, a researcher and co-host of the podcast “QAnon Anonymous,” said believers have continued to strain for explanations and concoct new theories, including that President Biden was filming his performances at a fake White House in Culver City, Calif.

View did not expect that the March 4 failure would lead many believers to denounce the cause.

“We often call the inauguration of Joe Biden the QAnon ‘great disappointment,’” he said. “Anyone who stuck with the QAnon movement after that is not just going to dislodge themselves because of something like this.”

In the two months since Katz and others warned of serious violence ahead of Jan. 6, there have been more than 300 arrests, extensive purges of QAnon followers on mainstream social media, crackdowns on fringe sites and internal friction among some organized groups, such as the far-right Proud Boys.

The Capitol, meanwhile, has been ringed by fencing topped with coils of razor wire, and defended by thousands of National Guard troops in camouflage. The Capitol Police requested Thursday that the National Guard stay for 60 more days after the planned end of their mission on March 12.

Major arteries through the nation’s capital remain closed. And no authority has announced a timeline for returning to the pre-siege days when tourists and neighborhood families strolled the Capitol grounds, snapped selfies and had picnics on the well-tended lawns — or, when Washington got its occasional snowfall of consequence, sledded merrily down Capitol Hill itself as police stood aside and watched.

The decision to lock down the Capitol even more aggressively on Thursday struck independent researchers as potentially excessive, based on the online intelligence they could access using open-source tools, such as following chat groups and extremist social media sites.

“They’re overreacting,” said Joel Finkelstein, co-founder of the Network Contagion Research Institute, a research group that studies online extremism and, like others in the field, had issued urgent warnings ahead of Jan. 6.

He said extremists may have embraced their power to disrupt ordinary events in Washington — and prompt intensifying security — by merely voicing threats in forums that law enforcement monitors.

“They’re going to get us chasing our tails everywhere,” Finkelstein said. “It’s going to make us more vulnerable.”

Peter Hermann contributed to this report.

EDITOR’S NOTE: This story quotes Travis View, co-host of the QAnon Anonymous podcast, without reporting that this name is a pseudonym, a detail View did not disclose to The Post when the story was written. That violates Post policy, which prohibits the use of pseudonyms except in rare cases and requires disclosure that a pseudonym is being used. View’s real name is Logan Strain.