The January 6th Committee revealed Secret Service communications from before the attack including one tip about the armed Proud Boys.
SCHIFF: “This email, for example, was an alert that the Secret Service received on December 24th with the heading “armed and ready. Mr. President.” According to the intelligence, multiple users online were targeting members of Congress, instructing others to "march into the chamber's on January 6th, and make sure they know who to fear. In this report received on December 26, the Secret Service field office relayed a tip that had been received by the FBI. According to the source of the tip, the Proud Boys plan to March armed into D.C. - “They think that they will have a large enough group to March into D.C. armed,” the source reported, and will “outnumber the police so they can't be stopped.” The source went on to say, ”their plan is to literally kill people. Please. Please take this tip seriously and investigate further.” The source also made clear that the Proud Boys had detailed their plans on multiple websites like theDonald.win.”
