The rest of this site exists to lay out the facts. This page exists to attempt to explain them. It will be up to the courts to determine if the explanations offered here are correct.
First, we review some of the most important facts that need to be explained...
1) Michael Flynn had to resign as National Security Adviser when it was revealed he was talking to Russia about removing sanctions, before taking office, and then he lied about it (including, apparently, to Vice President Mike Pence.) But he was not fired immediately -- he left 18 days after the White House was informed that his lies left him open to blackmail by Russia, and not until the media picked up the story. He pled guilty to lying about the call.
2) A Republican operative claimed he was working with Michael Flynn as he solicited stolen emails from hackers. And intelligence picked up Russian agents saying they were trying to get those emails to Flynn, and bragging about their influence over Flynn.
3) Paul Manafort had to resign as campaign manager when it was revealed he was getting cash payments from a pro-Putin party in Ukraine, and sought approval of his work for Trump from a Russian oligarch. He was later indicted.
4.) George Papadopoulos admitted in his guilty plea that his Russian contact "told defendant Papadopoulos about the 'thousands of emails' on or about April 26, 2016, when defendant Papadopoulos had been a foreign policy adviser to the Campaign for over a month."
5) Donald Trump Jr accepted a meeting he was told was "part of Russia and its government's support" for his father. Then kept quiet for a year about what was discussed and who else was there. He also exchanged direct messages with WikiLeaks. They told him that cooperating with them was "strongly in his interest." He did not report these exchanges. He did tweet out a link they sent him, and ask around about the owners of a website they said they had hacked.
6) Roger Stone admits he was in contact with Guccifer2.0 and WikiLeaks He knew about upcoming releases of stolen documents before they came out. He also received stolen DCCC data from Guccifer2.0 through a Republican operative named Andrew Nevins. In addition, a company hired by the Trump campaign reached out to WikiLeaks and offered to help them sort through the hacked emails.
7) Russian Ambassador Sergey Kislyak reported to his superiors that he was discussing substantive policy issues with Jeff Sessions in April, 2016.
8) In 2015, a Trump associate named Flex Sater wrote an e-mail to Trump's lawyer saying "Buddy our boy can become president of the USA and we can engineer it[...] I will get all of Putins team to buy in on this, I will manage this process.
And in light of those facts, a plausible worst case scenario...
Trump could have promised Putin he would:
1) Turn his back on NATO
2) Distance the US from European allies, especially German Chancellor Angela Merkel
3) Take the United States out of the Paris accord (Russia is a major oil and gas exporter)
4) Withdraw from trade deals which disadvantage Russia
5) Weaken the US government by fostering political division within the US
6) End the economic sanctions on Russia
Putin could have promised in return to help him win the presidency and help him financially by:
1) Hacking into Democratic Party servers and leaking the results
2) Sending millions of fake news stories about Hillary Clinton to targeted voters
3) Tapping into voter registration databases
4) Helping clear the way to build a Trump Tower in Moscow as well as financing other projects
5) Helping Trump repay his debts to foreign banks
6) Not revealing any incriminating information he may have had on Trump
It would seem likely that Paul Manafort, Michael Flynn, and possibly Jeff Sessions and Jared Kushner (as well as lower-level figures like Michael Cohen, Felix Sater, and Carter Page) were involved in implementing these plans, if they existed.
We lay out this explanation so as to be clear about the frightening scenario which seems very possible based on available evidence. That possibility should be enough to motivate Americans to take this issue very seriously, and support investigations. We do not claim that there is definitive proof that this is what happened, at this point. But it is consistent with the evidence we do have and cannot at this point be ruled out.
Below we link to some alternative explanations. The first are the explanations put forward by the Trump campaign and administration members who have been accused of collusion:
Trump lawyers say no income from Russia, with exceptions CBS (May 12th, 2017)
Trump Lawyer ‘Vehemently’ Denies Russian Collusion New York Times (August 30th, 2017)
Jared Kushner's statement on Russia to congressional committees CNN (July 24, 2017)
One year into the FBI's Russia investigation, Mueller is on the Trump money trail by Evan Perez, Pamela Brown and Shimon Prokupecz at CNN (Aug. 3, 2017) (Includes statements by representatives of Carter Page, Roger Stone, Michael Flynn, Paul Manafort, and Donald Trump)
Next some plausible explanations which, while they may involve some wrongdoing, are not as dramatic as the one outlined above.
Seven Theories of the Case: What Do We Really Know about L’Affaire Russe and What Could it All Mean? By Jane Chong, Quinta Jurecic, Benjamin Wittes at Lawfare (May 1, 2017)
The Innocent Explanation, Part #1 by Josh Marshall at Talking Points Memo (March 3, 2017)
Obama’s CIA chief just offered a Trump-Russia quote for the ages by Yochi Dreazen reporting on the testimony of John Brennan at Vox (May 23, 2017)
Trump Jr.’s Russia meeting sure sounds like a Russian intelligence operation by Rolf Mowatt-Larssen at the Washington Post (July 14, 2017)
An ex-CIA officer: the Trump Jr. meeting shows how the Russians exploit intelligence targets by Sean Illing interviewing Glenn Carle at Vox (Jul 14, 2017)
Trump's shady and inept campaign team was a perfect target for Putin's spies by Zack Beauchamp at Vox (Nov 1, 2017)
Another explanation has been put forward by a hacker who was tried in Russia for breaking into bank records. He confesses to the DNC hacking under the direction of the FSB, but distances himself from the Kremlin. It is unlikely the confession letter would have been leaked without Kremlin approval.
Putin Ordered Theft of Clinton's Emails from DNC, Russian Hacker Confesses by Cristina Maza at Newsweek (Dec. 12, 2017)
And finally, a couple of more in depth looks at that scariest scenario:
Oh, Wait. Maybe It Was Collusion. By John Sipher and Steve Hall at the New York Times (Aug. 2, 2017)
We’re Back to Manafort by Josh Marshall at Talking Points Memo (Aug. 4th, 2017)
The Art of the (Trump and Putin) Deal by Robert Reich (July 11, 2017)