The media's and the Democratic Party's obsession with the Trump-Russia conspiracy theory originates from events of April-June 2016.  Media operations by the Democratic Party and its media echo chamber have distorted not only the information about the relevant events, but even the background political picture of April 2016.

The DNC and Hillary constructed a conspiracy theory in which Putin ordered the hacking of the DNC network and subsequent mass distribution of the exfiltrated documents to help Trump beat Hillary.  Such actions were against Russian interests and very unusual for Russian intelligence.

Driven by their conspiracy theory, Hillary indulged in anti-Russian rhetoric, and the Obama administration drove relations with Russia to the worst point in the last 40 years.  Since the elections, the Democrats, the hard left, and the institutions owned by them have been pushing Trump to aggravate the conflict, started by Obama and Hillary.  But let's proceed in chronological order.

• Summer 2015 – The FBI warns the DNC about alleged Russian hacking.

The DNC ignores the warning.

• April 28, 2016 – The DNC discovers suspicious activity on its network.

...and calls its lawyer, Marc Elias.  On May 6, after more than a week of waffling, the DNC brings in cyber-security contractor CrowdStrike, selected based on affinity rather than on merits.  CrowdStrike "determines" there were two breaches and names the culprits behind them – Cozy Bear and Fancy Bear – claimed by CrowdStrike to be Russian elite hacker units of FSB and GRU, respectively.

The DNC refused to allow the FBI to access its computers, which it thought had been accessed by FSB and GRU.  Apparently, the FBI consented to be subordinate of FSB and GRU on this issue.

• June 12, 2016 – Assange of WikiLeaks declares that he's got internal documents from the DNC.

...and is going to publish them.  Surprised, the DNC and Hillary's campaign decide to pre-empt and even exploit this publication.

• June 14, 2016 – The DNC announces the network breach through a WaPo article.

CrowdStrike publishes alleged technical details on its website.  Both blame the Russian government.  The DNC says that only a few documents had been compromised, including opposition research on Trump.  This is an open invitation for WikiLeaks to publish that research.

• June 15, 2016 – Guccifer 2.0 claims the hack and posts several DNC documents on guccifer2.wordpress.com. 

Guccifer 2.0 wasn't known before that.  The opposition research is among the published files.  Independent analysts discover Russian fingerprints – the opposition research file shows an error message in Russian and had been last saved on a computer with Windows in Russian by Феликс Эдмундович.  Феликс Эдмундович refers to Felix Edmundovich Dzerzhinsky (1877-1926), the founder of the Cheka, the predecessor to the KGB.  Gotcha!  The ecstatic media form the narrative: all leaked DNC-Hillary documents come from the Russian government; Guccifer 2.0 is a front for a Russian intelligence operation.

Just a few weeks or days earlier, the DNC hired Fusion GPS, which hired Christopher Steele to produce dirt on Trump.  The outcome was a series of absurd pieces, which became known as the "Steele dossier."  It was called "a garbage document" by Bob Woodward.  The only known version of it was published by BuzzFeed.  The first "Steele report," dated June 20, makes bizarre claims and leaves the impression that Steele was unclear about what the client wanted him to write.

• July 16, 2016 – Guccifer 2.0 offers WikiLeaks about 1GB of leaked DNC documents.

Hillary, convinced that Guccifer 2.0 was a front for the Russian government, concludes that Putin had betrayed her.  I think that at that time she decided to invent a narrative that she is tough on Russia while Trump is Putin's puppet.  It was the summer of 2016, and people didn't know that the MSM had shifted from being biased to being shameless fake news.  Hillary's plan worked.

• July 18, 2016 – Hillary/DNC launch Trump-Putin conspiracy theory through WaPo and N.Y. Mag.

WaPo publishes an article titled "Trump campaign guts GOP's anti-Russia stance on Ukraine" (Josh Rogin), and N.Y. Mag "Is Donald Trump Working for Russia?" (Jonathan Chait).  The N.Y. Mag piece is a purported analysis.  It mentions the WaPo article, but it couldn't have been written in a half-hour.  Thus, these articles were part of a media operation by Hillary and/or the DNC.  The WaPo article falsely claimed that Trump's campaign had weakened the GOP platform regarding support for Ukraine against a Russian invasion and briefly mentioned Paul Manafort.

This DNC-Hillary media operation has achieved its apparent goal – establishing a crazy conspiracy theory of Trump-Putin collusion as a dominant media narrative.

• July 20-25, 2016 – Third Steele report mentions DNC files on WikiLeaks.

It's possible that Steele learned the new party line from the July 18 WaPo article, from copycats in other outlets, or directly from Hillary's boys.  None of the previous "reports" had mentioned a DNC hacking, WikiLeaks, Guccifer 2.0, or Paul Manafort.  But this one talked extensively about Manafort and the DNC documents on WikiLeaks.  Manafort and the DNC leaks had been placed together only in the WaPo article, which was largely retold in this Steele piece.  Examples:

"Suggestion from source close to TRUMP and MANAFORT that Republican campaign team happy to have Russia as media bogeyman[.]"

"TRUMP associate admits Kremlin behind recent appearance of DNC e-mails on WikiLeaks, as means of maintaining plausible deniability[.]"

Don't ask me which "Trump associate admits" something on behalf of the Kremlin – the whole Steele dossier consists of such rubbish.

• July 22, 2016 – A WikiLeaks dump reveals:

The DNC had cheated Bernie out of the votes in the primaries to make Hillary the presidential candidate.

• July 25, 2016 – The Democratic National Convention starts with a huge scandal.

The revelation of the dirty collusion between the Hillary campaign and the Democratic National Committee against Bernie rocks the Democratic National Convention.  Hillary blames Russia and Putin; the MSM echoes.  Hillary, the DNC, and the media become deluded into the consensus that Putin is behind Trump.  Now it's official: Hillary runs against Vladimir.

• July 26, 2016 – Fourth Steele report is almost entirely devoted to alleged Russian cyber-operations.

Note that the "Steele reports" were received by the DNC, and any piece might have been leaked to the media at any time after receiving.

• July 31, 2016 – FBI launches operation Crossfire Hurricane.

After watching the Democratic convention for days, reading media reports and Steele fantasies conveying the Democratic narrative, Peter Strzok decided to act.  Within two days, he and a few other Obama loyalists in the FBI started the operation Crossfire Hurricane, initially spying on Trump but then attempting a full-spectrum suppression of Candidate Trump and the Republican party.

Aftermath

Within a couple of weeks, CIA director John Brennan and other members of the Obama administration joined Crossfire Hurricane.  Obama-Hillary loyalists in DOJ, FBI, CIA, DNI, and DHS incited Republican senators against Trump, spread anti-Trump propaganda through media leaks, and even broadcasted support to the DNC-Hillary conspiracy theory of in a joint DNI-DHS statement merely a month before the elections.  These efforts continued after the elections and morphed into a coup d'état.

A longer analysis of the DNC leaks and origins of the Crossfire Hurricane from 2015 to August 1, 2016 is available from Leo Goldstein and the Science for Humans and Freedom Institute.