It's not unusual to hear House Democrats vow to "get to the bottom" of the Trump-Russia matter — as if the investigation by special counsel Robert Mueller, with 500 witnesses, 2,800 subpoenas, 500 search-and-seizure warrants, and nearly 300 records of electronic communications, was somehow unable to fully probe allegations that the Trump campaign and Russia conspired to fix the 2016 election.

What really concerns Democrats is that Mueller's investigation, conducted with law enforcement powers that Congress does not have, failed to establish any Trump-Russia conspiracy or coordination. And in doing so, Mueller exposed the fatal flaw of the Trump-Russia matter: It was driven entirely by the conspiracy/coordination allegation, which turned out to be false.

The backdrop of conspiracy and coordination made every Trump-Russia episode, including routine political activities, look sinister. The Trump Tower meeting looked ominous in the context of conspiracy and coordination. Donald Trump's public statements about Russia and its president Vladimir Putin looked incriminating. Michael Flynn's conversations with the Russian ambassador looked suspicious. And more.

If one believed that Trump and the Russians were conspiring or coordinating to influence the campaign, then any bit of information having anything to do with Russia and the Trump campaign looked portentous. The Russia frenzy became so intense that reputable news organizations published long stories cataloging all known "contacts with Russians" by anyone associated with the Trump campaign.

But it all depended on conspiracy or coordination. And when Mueller was unable to establish that any such conspiracy or coordination actually occurred, suspicious-seeming events could no longer be credibly cast as suspicious. The Trump-Russia bubble deflated.

That left Democrats with the allegation that the president obstructed the investigation. Some hope that will be enough to impeach Trump, but in recent weeks, they have discovered it might be a hard sell. While it is possible to pursue an obstruction allegation without an underlying crime, impeaching the president on that basis could prove politically difficult. So Democrats vow more investigation to "get to the bottom" of the Trump-Russia matter or perhaps find something else entirely unrelated to Russia to pursue against the president.

The post-Mueller debate on Capitol Hill shows just how critically important the conspiracy and coordination narrative was. Without it, everything has changed. So now that Mueller has formally closed his office and left the Justice Department, it is worth looking at how conspiracy and coordination — often referred to by the widely used word "collusion" — came to dominate American politics for the last three years. Was it a hoax? Hysteria? Or simply partisanship on steroids?

In June 2016, the Washington Post reported that "Russian government hackers penetrated the computer network of the Democratic National Committee." The paper also noted that "the networks of presidential candidates Hillary Clinton and Donald Trump were also targeted by Russian spies, as were the computers of some Republican political action committees." By the beginning of summer 2016, then, it was public knowledge that the Russians were up to something.

At the same time, and especially as the Republican and Democratic conventions approached in July, Democrats began suggesting that Trump might be up to something with the Russians. Candidate Trump had expressed admiration for Putin and indicated that, if elected, he would like to have better relations with Russia. Trump also vowed to press NATO countries to pay more for their own defense, a position Trump's adversaries interpreted as pro-Russian. Trump had also hired Paul Manafort, who had extensive business ties to pro-Russian candidates in Ukraine, as his campaign chairman.

In the days leading up to the Democratic convention, the Clinton campaign and its allies in the press saw Russia as a potentially valuable weapon for attacking Trump. On July 20, the New York Times' Andrew Rosenthal wrote a column headlined, "Is Trump Obsessed With Putin and Russia?" Two days later, Rosenthal's Times colleague Paul Krugman wrote a piece entitled, "Donald Trump, the Siberian Candidate," in which he asked, "If elected, would Donald Trump be Vladimir Putin's man in the White House?"

That same day, July 22, Wikileaks released emails from the Democratic National Committee. Two days later, on the 24th, Clinton campaign manager Robby Mook went on television to claim that not only was Russia behind the hack — that was later proven true — but also that the Trump campaign was in league with Russia.

"Donald Trump changed the Republican platform to become what some experts would regard as pro-Russian," Mook told ABC News, referring to a just-published Washington Post story that reported, incorrectly, that Trump aides had weakened the portion of the GOP platform regarding Russia and Ukraine.

"He has praised Vladimir Putin," Mook continued. "It's troubling."

Also on July 24, the Times published a news story headlined, "As Democrats Gather, a Russian Subplot Raises Intrigue." "Even at the height of the Cold War," the paper reported, "it was hard to find a presidential campaign willing to charge that its rival was essentially secretly doing the bidding of a key American adversary. But the accusation is emerging as a theme of Mrs. Clinton's campaign."

In the next few days, there were reports that U.S. intelligence agencies had confirmed Russia's responsibility for the hack, followed by the first appearances of the C-word.

"Donald Trump said he has 'never spoken' to Vladimir Putin amid allegations that his campaign colluded with the Russian president," ABC reported on July 27.

"The Clinton campaign is basically saying that there's collusion between Trump and Russia," the New York Times' Maggie Haberman said on CNN on July 29.

The reporters did not present the allegation as fact but rather as news that Clinton people were accusing Trump of colluding with Russia. Over the next few months, the accusations grew and grew and grew.

At the same time, Marc Elias, a lawyer for the Clinton campaign and the DNC, retained the opposition research firm Fusion GPS, which in turn retained the former British spy Christopher Steele to search for dirt on Trump and Russia. On June 20, 2016, Steele finished the first installment of what became known as the dossier. It was a blockbuster, alleging that Russia had been "cultivating, supporting and assisting" Trump for at least five years, that Trump had accepted "a regular flow of intelligence from the Kremlin," and that Trump was the target of blackmail since Russian intelligence services taped him watching a kinky sex act with prostitutes in a Moscow hotel room in 2013.

According to Russian Roulette, the book by reporters Michael Isikoff and David Corn, Steele sent the first installment to Fusion GPS in June 2016. Fusion, in turn, "gave Steele's reports and other research documents to Elias," according to a Washington Post account. And Elias briefed the Clinton campaign.

"We were getting briefings that were put together by the law firm with information," Mook recalled in an interview with CNN in late 2017. "So our internal team was presenting information, our lawyer was presenting information, you know, and we — and we sort of learned things in pieces."

So as Clinton and her aides pushed the collusion narrative, with the help of an enthusiastic press, campaign officials were also being briefed on the newest, freshest allegations from Steele.

The problem, of course, was that the allegations were not true. Steele also gave his reports to the FBI, which tried to verify them "line by line," according to former FBI general counsel James Baker. It did not succeed. Nearly three years later, the Mueller report failed to corroborate any of the dossier's serious allegations. It was wrong at best, a fraud at worst.

The public did not know what was happening behind the scenes. All they heard — if they watched cable TV — was collusion, collusion, collusion. After the election, the allegations consumed reporting on the Trump transition and then the Trump presidency — especially after the dossier was published in its entirety in January 2017, following the decision by the nation's top intelligence chiefs to brief President-elect Trump on parts of it.

After that, each new revelation that appeared in the press — Flynn, Manafort, Trump Tower, Michael Cohen, all of it — appeared in the context of collusion. Ordinary events became shady scheming against the backdrop of Trump-Russia collusion.

As that was happening, Mueller was trying and failing to establish that collusion ever occurred. From interviews with various players in the investigation, it now seems clear that by the end of 2017 Mueller knew that he could not establish conspiracy or coordination. That part of his investigation effectively ended when 2017 did.

Yet Mueller continued his investigation for more than a year, mostly focusing on obstruction allegations. Collusion as a topic of investigation might have been dead and gone by that time, but the fact that the Mueller investigation was still going on kept the collusion narrative alive. And that fed the public perception that events Mueller secretly knew were not part of a collusion scheme were still in some way suspicious.

The collusion narrative became so entrenched in the minds of some commentators that even when the Mueller report was made public, with its repeated statements that "the investigation did not establish that the [Trump] campaign coordinated or conspired with the Russian government in its election-interference activities," some simply would not accept the verdict.

So now Democrats are promising to carry on, to find that thing — collusion — that Mueller could not find. At the same time, others, most notably Attorney General William Barr, have decided to find out how the whole unhappy episode started and what role the nation's intelligence and law enforcement agencies played in the process. It is time to know what happened.