House lawmakers cancelled their sessions for the day and security officials tightened up their perimeter due to a "possible plot" against the site, Capitol Police said.
The threat coincides with chatter among far-right QAnon groups online, where some suggested that Trump was poised to retake the presidency from President Joe Biden, who beat him in the 2020 election. They reportedly circled March 4 because it was the original presidential inauguration day until 1933.
The date has been circulating among QAnon message boards since shortly after Biden's inauguration on Jan. 20, according to BBC News.
QAnon appears to have seized on the March 4 date based on a bit of history and a misinterpretation of the U.S. Constitution, Vox reports. The baseless theory stands on a few different fantastical stories, including something about clones, body doubles and graphic fake-outs — all typical fare for the wide-ranging hoax.
However, some leaders among the group have already tried to distance themselves from the date, dubbing it a "false flag." They said something similar after the U.S. Capitol riot on Jan. 6, which involved many high-profile QAnon figures and other supporters.
The conspiratorial soul-searching has become increasingly common among members of QAnon, many of whom have struggled to grasp the reality of Trump's election defeat.
The fantastical movement imagines Trump as a warrior for God who was chosen to root out a cabal of Satan-worshipping cannibalistic pedophiles within the Democratic Party and Hollywood. Adherents believed that Trump would punish these imaginary villains and return for a triumphant second term in office after a violent "storm."
The movement sprang out of an older conspiracy theory about pedophiles, and is based on a series of messages posted online by a figure named "Q." That person claimed to be a government insider who was working with Trump. They posted several cryptic messages during his term, but have fallen silent since the last message in December, Insider reports.
QAnon believers have clung to Trump's false claims that he actually won the presidential election that he lost in November, and they have imagined several last-minute comebacks for their defeated leader in recent months.
None of those comebacks have happened, but the conspiracy theory has survived in part by repeatedly moving its goalposts, according to Julian Feeld, an expert on the hoax and host of the QAnon Anonymous podcast.
"One of the things that defines QAnon is the "baking,' which means the interpretation," he told Global News Washington Bureau Chief Jackson Proskow. Feeld explained that QAnon believers will re-imagine their movement whenever it clashes with reality, "baking" new belief systems that sometimes become part of their canon.
"(They) have a lot of different divergent thoughts," Feeld said. "All of them obviously are manifestations of cognitive dissonance around their disappointment, and their inability to grasp that the plan they believe in … has simply not materialized."