Journalists have been revealing connections between the campaign and Russia on a sometimes near-daily basis.
So what have all these ongoing Russia investigations found so far?
A lot, but at the same time, no one big thing we can point to that indicates a sure direction of the investigation.
"What we can take away is we are in the midst of a major investigation with foreign policy ramifications," said Jeffrey Jacobovitz, a white-collar lawyer who has defended Clinton Administration officials.
Here are all the things we know about the Russia investigation to date, ranked in order of their perceived magnitude:
1. Two Trump officials pleaded guilty to lying to the FBI about their connections and conversations with Russians.
Trump campaign aide George Papadopoulos pleaded guilty to lying about his attempts to connect the campaign and Russia; top campaign officials knew he was reaching out to Russia.
And, the biggie: Former National Security Adviser Michael Flynn admitted he lied to the FBI about the nature of his conversations during the transition with the Russian Ambassador to the US. (The two talked about political issues, such as US sanctions on Russia, which Flynn originally denied.)
Now Flynn is cooperating with the Special Counsel, which could be a big deal. As the Washington Post reported: "If anyone on the campaign coordinated with the Russians in their efforts to interfere with the election, Flynn would probably have been aware."
2. Former Trump campaign chairman Paul Manafort and his deputy, Rick Gates, were also indicted in Mueller's investigation. They pleaded not guilty to charges related to money laundering and making false statements related to their past work advising a pro-Russian political party in Ukraine.
3. The special counsel is looking into the President himself. He is specifically considering whether Trump obstructed justice by abruptly firing former FBI Director James Comey.
4. Trump's lawyer said the President knew Flynn had probably given the FBI inaccurate information about his conversations with the Russian ambassador. Trump found this out a few weeks before Comey claims the President asked him to go easy on Flynn. Legal experts say if Trump knew Flynn had lied, it could explain why he allegedly asked Comey to "let this go". Trump denies making the request.
5. Comey all but accused the President of obstructing justice. He testified under oath to Congress that he believes Trump fired him because of the Russia investigation. "It's my judgment that I was fired because of the Russia investigation - I was fired in some way to change, or the endeavour was to change, the way the Russia investigation was being conducted," Comey said. "That is a very big deal."
6. Emails revealed Donald Trump Jr., Jared Kushner and Manafort met with a Kremlin-connected lawyer in Trump Tower in New York. The meeting occurred during the campaign on the premise that she had dirt on Hillary Clinton as "part of Russia and its Government's support for Trump." Legal experts said that this likely crossed the legal line on collusion.
7. When that meeting became public knowledge in 2017, Trump dictated his son's misleading statement on what it was about. Trump told him to say it was primarily to discuss policies on Russian adoptions. It's still not clear if the President knew about the meeting when it happened.
8. Various members of the Trump campaign and Administration have repeatedly not been forthcoming about their Russia connections. Two high-profile examples: Kushner didn't include his meetings with Russians on his security clearance, and Attorney-General Jeff Sessions had to re-testify to Congress that he did have conversations with Russian Ambassador Sergey Kislyak during the campaign despite indicating under oath he hadn't.
"They either denied or omitted their meetings with Russians," Jacobovitz said.
9. During the transition, Kushner suggested establishing secure communication lines between Trump officials and the Kremlin via Russian diplomatic facilities. That's according to the Russian ambassador, who relayed this request to his bosses in Moscow.
10. Mueller has interviewed two dozen current and former Trump aides. They include Kushner, former chief of staff Reince Priebus, former press secretary Sean Spicer and current communications director Hope Hicks.
11. Trump jnr exchanged private messages with WikiLeaks during the campaign. That occurred at the same time the website was publishing hacked emails of Democratic National Committee staffers and Clinton campaign chairman John Podesta.
12. The Russians extensively used Facebook and Twitter to interfere with the election.
Here's one big thing we don't know: whether any of this implicates the President or his campaign. It might. Or it might not. And we may never uncover a smoking gun, legal experts say.
"I think it's unlikely to be the kind of case where there's one event or one development that is so significant that it blows the story out of the water," said Jens David Ohlin, vice-dean of Cornell Law School.
"It's a slow accumulation of dozens of different events, conversations and moments that are pieced together. And then, when you look at the whole story, you say: 'Hey, wait a minute. Something is going on here'. "
Throughout all of this, Trump has maintained this entire Russia investigation is a hoax.
He also hasn't fully acknowledged the US intelligence community's assessment that Russian President Vladimir Putin ordered Russia to interfere, saying he believes Putin when he claims Russia didn't meddle.
Ohlin says he has a sense that the Special Counsel's office is in the middle of the investigation, and we could have a long way to go before the outstanding questions are answered: "I'd say that the investigation is going to be measured in years, not months."
