The FBI-Homeland Security intelligence bulletin circulated at midnight Tuesday is ominous, but entirely predictable, given widely published reports of far-right chatter over the past several weeks:  It alerts local law enforcement officials that extremists may try to breach the U.S. Capitol Thursday and attack Democratic lawmakers. 

The warning is based on a malevolent fantasy spread by followers of Qanon, the cultish pro-Trump movement—that Donald Trump will reemerge to take power as the rightful president on March 4, which was Inauguration Day until 1933.  Preposterous, but the FBI has learned not to dismiss any threat, no matter how irrational.

“It does not take an armed takeover” by an organized group to do a lot of damage, says Tom O’Connor, an FBI agent who investigated suspected domestic terrorists for 23 years. “It takes one person who believes they need to act. How possible is that, I ask you?”

Dead easy, as the FBI knows from the many cases in which lone ac…