The sight of thousands of men and women storming the Capitol building last Wednesday may have been shocking, but it shouldn't have been a surprise.
In 2008 the Republican party opened the gate to precisely this event.
Back then, the presidential campaign of John McCain was flagging; the Republican standard bearer was trailing Barack Obama in every poll and he needed something to shift momentum.
McCain wanted to make a bold call and choose the former Democratic, then Independent, senator Joe Lieberman as his potential vice-president.
Lieberman, as Al Gore's former running mate, would have been a symbol of McCain's commitment to bipartisan ideals.
The idea went as far as gaining the approval of Lieberman before it was accidentally leaked, and subsequently torpedoed by influential conservative figures such as Karl Rove and Rush Limbaugh.
Fearing a contested convention, McCain abandoned the plan. A week from the Republican convention he'd no running mate in mind. In desperation, his campaign turned to an unknown Alaskan governor - Sarah Palin.
Palin was ultimately a disastrous pick who was ridiculed for her gaps in basic knowledge and untrusted by moderate voters.
But she was a revelation with the Republican base.
The hard-right figure was enthusiastically received at huge rallies, where she accused Barack Obama of being an elitist "palling around with terrorists". Supporters at her rallies wore T-shirts declaring "no Commies" and shouts of "kill him" were heard when she mentioned Democrats. The crowds also often chanted "shame" at assembled media.
That VP pick marked a sliding doors moment for the Republican party.
At an electoral crossroads between moderation or fundamentalism, it chose the latter - and it led directly to the scenes of Wednesday.
Thousands of would-be protesters, riled up by elected Republicans, invading the Capitol. Members of Congress forced to flee instead of certifying election results. A Republican president speaking of his love for those attempting an inept rebellion.
All human beings are susceptible to delusions, tribalism and populist mobilisation. It's a fundamental evolutionary glitch in our make-up - one that's been exposed time and again throughout history. It's a glitch that means democracies need gatekeepers to survive long term (as described in How Democracies Die by Harvard professors Steven Levitsky and Daniel Ziblatt).
Traditionally in the US, those gatekeepers have been the political parties and the press. The party establishment vets candidates and removes demagogues; the press makes them do so by holding them to account and ensuring an informed public.
The Republicans abandoned their role as gatekeepers just as social media's rise allowed subversive elements to start sidestepping the fourth estate and create their own realities. Once that happened, they lost all control.
Because once a person is convinced something is true, everything changes. However baseless, however delusional, however unhinged that belief; once it becomes the accepted reality for the individual, everything is seen through that lens. And actions that seem illogical to most become internally logical and consistent. Everything fits together.
The man who cried "they don't get to tell us we didn't see what we saw" (meaning evidence of voter fraud) on his way into the Capitol building truly believes they saw clear evidence of widespread voter fraud.
Fed on an infinite diet of self-selected conspiracy theories, in their own eyes, these rioters' actions are as justified and as necessary as the initial American War of Independence or any modern revolutionary protest. They're delusional, but not cynical.
That has to be an important consideration for the Biden administration.
Tackling the sources of online mis- and disinformation has to be an immediate aim. Their response can't just tackle the specific actions of those involved in the botched coup; they have to go further to tackle the impulse that drove the actions.
The specific actions need to be prosecuted, of course. The initial response was shocking in its ineptitude and jarringly unusual in its restraint. But this has to only be the start. The violent actions seen on Wednesday are merely a symptom of a deeper disease.
We're no longer just talking about the active lunatic fringe. In a YouGov poll taken just hours after Wednesday's dramatic events, 45pc of registered Republican voters who responded approved of the storming of the Capitol.
Once inaugurated, Biden must bring the weight of his public influence to bear on the social media platforms which have been glacially slow to react to this threat.
In the run-up to the November election, perhaps sensing the momentum was with Biden, these companies began to react, tagging Trump's tweets and posts as misinformation and limiting their spread. Last week, his open praise of the rioters led to his indefinite suspension by Facebook and Instagram, followed on Friday by his banishment from Twitter.
Biden and the Democratic establishment must ensure, through influence and regulation, that within seconds of the new pretender to Trump's populist throne implementing a similar playbook, suspension happens - and sticks.
An even greater challenge faces the remaining 'traditional' Republicans: how to regain control of their party and retake their positions guarding the gate.
Now is their moment. Trump is at his lowest ever ebb. The incompetent legal challenges to the election results have meant he's suffered the same defeat, multiple times - undermining his brand as a winner that his supporters cling to. The social media bans threatens the destruction of his final bully pulpit, reducing his threat to other Republican politicians.
Most importantly, the double Republican loss in the Senate run-off elections in Georgia has undercut the argument for the party to follow his approach long term.
Republican power brokers, and key Trump enablers like Mitch McConnell and Lindsey Graham have now deserted the US president. It's a sign that they no longer see a link to Trump's wing of the party as a net benefit.
It's possible the scenes in the Capitol will, therefore, be seen in hindsight as the last sting of a decapitated movement. But only if both parties make the courageous decision to prioritise different forms of moderation. America is at a new crossroads. They have to choose the right path.
Lorcan Nyhan is head of training at the Communications Clinic