Mr. Mueller's indictments show that Russian agents interfered with the 2016 election by sowing discord on social media and hacking and disseminating Democrats' emails. Yet it now seems wiser to point to our intrinsically American shortcomings, more than Russian interference, for Mr. Trump’s victory. And in rushing to blame Russian collusion, we have wasted time and political opportunity that we might better have spent reckoning with how to prevent a Trump-like catastrophe from happening again.

I’m spelling all this out starkly, because in the spinning to come, it will be all too easy to lose yourself in misdirection. If you are a liberal, you might be especially tempted to give in to the aggrieved and embarrassed #resistance-tweeting punditocracy now throwing up endless reasons for downplaying Mr. Mueller’s finding: We still haven’t seen the whole report! The attorney general is a toady! Don’t forget about all those other investigations of all those other crimes!

These are all important points. But don’t overlook the headline finding. Like the Trump victory itself, Mr. Mueller’s no-collusion conclusion should leave a mark. It lands like a rotten egg on a political and media establishment that had gone all-in on its own self-serving — and wrong — theory of the case. Before we embark on yet more investigations, it is worth examining, now, why the collusion fantasy proved so irresistible to so many of us — and what we all might have done with our time instead.

Here’s my theory: Collusion was a seductive and convenient delusion. For many Americans, the simple truth that Mr. Trump really had won was too terrible to bear. The ease with which a racist, misogynist, serial con man had slipped past every gatekeeper in American life suggested something deeply sick at the core of our society.

In particular, Mr. Trump’s win pointed to tectonic failures within the mainstream news media, whose leading brands had fanned the showman’s rise with copious television coverage; indulged his every gimmick with yet more attention; and elevated his opponent’s trifling email-management kerfuffle into a scandal of world-historic import.