The end of the Robert Mueller investigation has demolished Democrats' mythology about the 2016 election. That should force them to confront some unpleasant truths about what has happened to their party since President Trump's election — and, more to the point for 2020, it should force enough introspection to prevent a repeat performance.

The idea that Trump colluded with Russia to defeat Hillary Clinton was appealing to many Democrats in the same way any conspiracy theory appeals to the confused: It seemed to explain the inexplicable, with paranoia providing enough elasticity to gloss over any plot holes. The theory's most attractive feature was the near-impossible task of debunking it.

And few realities were more confusing than Trump's win via victories in key Democratic states like Wisconsin, Pennsylvania, and Michigan, all of which went Republican for the first time in decades. How could an uncouth loudmouth like Trump defeat a polished professional like Clinton? Divine intervention — or at least some sort of outside intervention — was the only answer. Real Russian efforts to undermine confidence in the election only fed this confusion.

But as an answer to the inexplicable, the Russia-collusion theory was never airtight. Moscow did meddle in election advertising, but its efforts were surpassingly small in scale and not particularly skillful. A $25 million investment in social media trollery was miniscule in an election in which the major-party candidates and their allies spent nearly two billion dollars. The other Russian intervention — hacking the Democratic National Committee and Clinton campaign manager John Podesta — was far more significant, but just as distant from the Trump campaign proper.

For two years, Democrats used Russian interference to explain away their loss in 2016. Even as Mueller prepared to send his report to Attorney General William Barr, Democratic leaders like House Intelligence chair Adam Schiff (Calif.) insisted evidence of collusion was already obvious. Former CIA Director John Brennan confidently announced earlier this month that Mueller was about to drop indictments on Trump and his inner circle.

Then Mueller broke the Russia-collusion spell. "The Special Counsel did not find that the Trump campaign, or anyone associated with it, conspired or coordinated with the Russian government in these efforts," Barr's summary to Congress declared, "despite multiple offers from Russian-affiliated individuals to assist the Trump campaign." No other indictments will be sought. The conspiracy hypothesis for the 2016 election is dead.

This leaves much of the Democratic Party with egg on its face. Credibility in may be a real problem for 2020 — not only for the presidential contenders but also for their organizers and surrogates. A wounded media may be less willing to carry their water on anti-Trump arguments after this burn.

Yet Democrats' biggest problem is the mythology. If Trump didn't play dirty, just how did he beat Clinton? Answering that accurately — a necessity for 2020 strategy — requires facing the truth: Clinton lost because she was a terrible candidate with an unwise campaign focused on identity, entitlement, and the progressive activist agenda.

On paper, Trump should have been easy to beat. He had poor message discipline, a lifetime of scandalous behavior, and an agenda that cut against the historic march of his own party. What Democrats and Trump's primary opponents alike failed to understand was his instinctual connection to disaffected Middle America. His celebrity and anti-establishment message resonated with millions of frustrated and disappointed Americans outside of the media-academic bubbles. He captured the spark of populism on the right with an authenticity no GOP insider could match.

Clinton too embodied that insiderism, a liability exacerbated by the hacked DNC email evidence of her party's unfair marginalization of challenger Sen. Bernie Sanders (I-Vt.). Clinton's persistent focus on herself — her gender and her entitlement to the White House after her primary loss in 2008 — played to the same weakness. Rather than take the obvious opening to appeal to the center, the Clinton campaign moved hard to the left in response to Sanders' nearly successful populist insurgency. And worst of all, Clinton followed Republican Mitt Romney's 2012 playbook in conducting a national message campaign instead of imitating former President Obama's groundbreaking targeted organizing from 2008 and 2012.

These missteps together produced a significant recession in the Democratic vote in vital states. As I've noted previously, Clinton lost Wisconsin, Michigan, and Pennsylvania far more actively than Trump won them. He didn't expand the Republican footprint significantly in any of these states, a truth obscured in the GOP's own mythology of 2016. He simply held his ground while Clinton energetically squandered Democrats' "blue wall" advantage with her self-centered, too-progressive messaging.

In 2020, Trump will take the field in far more comfortable conditions than he enjoyed in the 2018 midterms. His critics' credibility issues will offer ample space to rail against the "swamp" and its "evil," "treasonous" creatures. If Democrats refuse to shut up about Russian collusion, spending more time attacking Trump than connecting to voters, they'll doom their presidential hopes with a repeat of the mistakes of 2016. That will be especially true if their candidate trods the same progressive-identity path Clinton walked ... right off the plank.