The conspiracy theory that President Donald Trump’s 2016 presidential campaign colluded with the Russian regime of Vladimir Putin is nearly three years old.

Two years of investigation by Special Counsel Robert Mueller — whose report is anticipated any day now — and by numerous congressional committees have failed to produce evidence to substantiate the claim.

Yet many Democrats, and journalists, remain mesmerized by what is almost certainly a hoax.

The “Russia collusion” hoax has undermined the new administration and divided the country. But perhaps its worst damage has been to the Democratic Party itself.

As Shadi Hamid noted in the Wall Street Journal last year, the part of the Democratic Party that was most shell-shocked by the results of the 2016 presidential election was the center-left, not the far-left. And it is the center-left, not the far-left, that has been most obsessed with “Russia collusion.”

The “progressive” wing of the Democratic Party could understand Trump’s win because he had appealed directly to the working-class voters they warned the party establishment not to ignore, and talked about issues, like trade, that Sen. Bernie Sanders (I-VT) had highlighted in his own campaign.

Left-wing filmmaker Michael Moore predicted, in October 2016 — before James Comey announced a renewed investigation into Hillary Clinton’s emails, which she also blamed for her loss — “Trump’s election is going to be the biggest ‘f*** you’ ever recorded in human history.”

Because they had a theory about why Trump could win, the far-left was less surprised when he did so. (Some may even have voted for Trump, quietly, in the Upper Midwest.) When he won, the activists of the far-left were stunned but not stupefied. They were able to organize protests, to recruit candidates, to raise funds, and to canvas support.

The center-left party establishment had the resources to push back, and to maintain control. What it lacked was the will, the leadership, and ultimately the composure. The center-left convinced itself that the election must have been stolen — by Comey, or by Russia, or by “fake news” — and that Trump represented a new Hitler, a potential dictator. Impeachment became an obsession for major party donors and even among the intellectuals in the Clintons’ orbit.

The party establishment became so obsessed with Trump, Russia, and impeachment that it failed to develop an alternative vision, a set of policies that could compete to provide a better life for ordinary Americans (who are, it turns out, doing better than ever under Trump). Into that vacuum came Alexandria Ocasio-Cortez, Pramila Jayapal, and other far-left ideologues offering utopian socialist policies like the “Green New Deal” and “Medicare for All.”

Terrified of the momentum the young progressives had seized, the party establishment hardly pushed back. Instead, almost all of the presidential candidates embraced the new, absurd policies.

Republicans were delighted: Democrats had provided the perfect foil. Suburban voters elected Democrats to run the House in 2018 partly as a rebuke to Trump’s disruptive style. But Democrats have only delivered more disruption — and promise revolution in 2020.

Former Vice President Joe Biden, still on the sidelines, represents the last hope of the party’s moderates, the only candidate who can bridge the growing divide between liberal and left. But between Bernie and Beto, there is not much room left for another white male.

While obsessing about “Russia collusion,” the Democratic establishment has lost control of its party. Only defeat will allow new, wiser liberals to set aside the far-left and restore sanity.

Joel B. Pollak is Senior Editor-at-Large at Breitbart News. He is a winner of the 2018 Robert Novak Journalism Alumni Fellowship. He is also the co-author of How Trump Won: The Inside Story of a Revolution, which is available from Regnery. Follow him on Twitter at @joelpollak.