Idea: A belief, option, or doctrine; a characteristic or controlling principle.
Organization: A group of persons associated together for a common purpose and having a set of rules which specify the relations of the individual members to the whole group, and to non-group members.
With that, we can parse Joe Biden’s advice not to worry about unorganized ideas:
“Antifa is an idea, not an organization.“.
So, what did Mr. Biden mean? It seems clear he was trying to minimize growing national disquiet over Antifa’s America-threatening ideas: Antipathy to free speech, contempt for free markets, abhorrence of private property, hatred for the Constitution, and disdain for the rule of law. Biden’s statement is an acknowledgment that Antifa ideas are threats (which he didn’t denounce, either, you’ll note), and the implication that violence, arson, and murder in the name of those ideas isn’t a problem because they aren’t co-ordinated.
Mr. Biden to the contrary notwithstanding, there is ample evidence of organization in Antifa’s implementation of a totalitarian agenda.
Even the New York Times gets it:
The Truth About Today’s Anarchists
[D]ocuments the “systematic, online mobilization of violence that was planned, coordinated (in real time) and celebrated by explicitly violent anarcho-socialist networks that rode on the coattails of peaceful protest,” according to its co-author Pamela Paresky…
“The ability to continue to spread and to eventually bring more violence, including a violent insurgency, relies on the ability to hide in plain sight — to be confused with legitimate protests, and for media and the public to minimize the threat,” Dr. Paresky told me.
As in, “It’s just an idea.”
That idea helps them hide in plain sight. I’m so old, I remember when “Communist cell” was much the same thing.
Then, there’s a Rutgers study with the page heading, NETWORK-ENABLED ANARCHY ● A CONTAGION AND IDEOLOGY REPORT: A fact check on Mr. Biden’s disingenuous and ignorant effort. Emphasis mine:
“Three tactics characteristic of extremist online communities have allowed them to become influential in recent years: 1) they use memes as propaganda , 2) they employ sophisticated communication networks for both planning and recruiting, making use of both fringe and private, online forums , and 3) they organize militias, and inspire lone wolf actors for violent action [3, 4].
On social media, memes—images, videos, and/or slogans—permit extremists to plant hateful , antisemitic  and/or revolutionary  ideas in the public eye. Often, they are disguised with humor or through using coded language, and originate in online forums [5, 6]. The somewhat private nature of these forums allows extremist groups to use them to shield themselves from view while sharing extremist ideas and coordinating action. . Finally, many extremist movements, from radical Jihadi to libertarian-anarchists, now use social media memes and other propaganda to recruit for militias with apocalyptic and revolutionary ideology (such as global Jihad or apocalyptic confrontations with police) [3, 9]. Organized violent networks that support these ideas generate both lone-wolf  and cell-like  attacks against law enforcement and the general public.
During opportune moments of vulnerability, these groups take advantage of social unrest over major events such as the Covid lockdowns and George Floyd’s killing. The target of much of the recent outrage in these events has been the most visible institutional manifestation of state authority and raw power: the police .”
Rutgers tells us there are such groups on the Left and the Right, but the examples are almost all on the Left. And the congruency of lockdown protests with Floyd events suffers from the fact that there have been no murders, looting, or arson in any lockdown protests.
Finally, here’s an inside look at Antifa organization.
The Conservative Trans Woman Who Went Undercover With Antifa in Portland
“There are different types of bloc organization styles. The building block of antifa is what’s called an affinity group, people you live and work with and trust and know in real life. All the planning is done within that closed bloc, and they don’t let everyone know [what they’re going to do]. I didn’t know that they were going to burn the Portland Police Association when I joined. What they did was put a call out that said, “Anyone show up in black that night at this place, and you can join the action.”
That’s called a semi-open bloc. The planning is done within the closed group, but anyone who’s dressed in black can come join the action. If you know what you’re looking for, you can spot affinity groups that are working together. One thing they’ll do sometimes is have written agreements with other protest organizations that aren’t in black bloc. I know of one from Berkeley that illustrates this: “We agree that to not take pictures of anyone in antifa.” It will say that literally in writing, so everyone’s working together. It’s like a combined arms type thing, almost like the military. They work together and are mutually reinforcing…
I describe it as an open-source networked insurgency. They were incredibly efficient. They hit a target and vanished into the city and got away. Basically, they’re like skirmishers: They come in, they attack the cops, they get out.
Antifa goes for a certain type of violence, a mid-level violence. Most people aren’t practiced in violence, and what they’ll do is, they’ll either back down or they’ll overreact. Antifa basically as a group does the equivalent of just pushing someone on the shoulder, and again, and again…
It’s really interesting. I did a breakdown of the Grant Park video, the tech they had. And that was freaking incredibly sophisticated. This is Grant Park in Chicago, when they attacked the statue and put like 49 police officers in the hospital. [Tonight] was so much like this, in terms of operational sophistication, how coordinated everything was.
Let me explain that a little more. People keep looking for a chain of command, and you don’t necessarily need that, as long as everyone understands a basic level of instruction it works…
[The media] play these little word games, “Oh, antifa doesn’t exist.” Yes and no. It’s not an organization where you have to sign up for a membership. It’s one of those things where it’s just a loose-knit network of people.”
Just an idea?
Antifa is a set of ideas in the same way the Democratic Party is a set of ideas. Antifa’s doctrine is just more narrowly focused. They don’t pay lip service to the Constitution, but both organizations would like Article V repealed and replaced with a popular vote Constitutional Amendment process; of which the first results would be repeal of the Second, Ninth and Tenth Amendments.
Not an organization?
Antifa is an organization, it just doesn’t have an official leader, like the Democratic Party.
Antifa, moreover, is an organization whose members received bail money from Biden and Harris staffers. Antifa is an idea supported by Democrat officials like Ted Wheeler, Jenny Durkan, Keith Ellison, Jay Inslee, John Thompson (the MN state District 67 rep), Alexandria Ocasio-Cortez, Ilhan Omar, and Ayanna Pressley. To name a few.
Antifa is the meme that ties anarchists together. That is, the organizing principle for overthrowing the Constitution.