Souvenir matryoshka dolls decorated with Donald Trump, U.S. President-elect, left, Vladimir Lenin, former Communist Party founder, center, and Vladimir Putin, Russia’s president, sit on display at a Christmas market on Red Square in Moscow, Russia, on Wednesday, Dec. 28, 2016. President-elect Donald Trump said Wednesday that the U.S. should move on rather than retaliate against Russia for interfering in the 2016 election, with the Obama administration expected to soon take action against Moscow. (Photographer: Andrey Rudakov/Bloomberg)

By now, few American elected leaders -- other than President Donald Trump, on occasion --dispute that elements of the Russian state interfered in the 2016 U.S. presidential election. What remains unproven is whether anybody from Trump’s winning campaign assisted in that interference. Though Trump dismisses talk of collusion as “a total hoax,” a wide-ranging criminal investigation has produced indictments against 26 Russian nationals and four former Trump advisers, among others. Though none of the Americans has been tied directly to Russian meddling, the cases against them have dropped at least some hints of the Trump campaign having wanted to play ball.

1. What exactly did Russia do?

U.S. intelligence agencies concluded that Russian President Vladimir Putin personally ordered a campaign to undermine “public faith in the U.S. democratic process” and the candidacy of Trump’s opponent, Hillary Clinton, and that along the way, Putin and his government “developed a clear preference” for Trump. Russia’s efforts included hacking and leaking emails that undermined Clinton’s campaign, and using phony accounts and advertising on Facebook and Twitter to sway American public opinion. A U.S. Senate committee investigating Russian meddling concurred with the findings of the intelligence community. Putin now says he did in fact want Trump to win the election, because Trump had expressed a desire to improve U.S.-Russian relations. But he, like Trump, denied any collusion.

2. What’s still not known?

What if anything Trump or his team did to solicit, encourage or participate in Russia’s effort. This is where Trump has drawn the line, swearing that no evidence will emerge of collusion. But Trump’s opponents say some compelling clues are already out in the open. A former Trump foreign policy adviser, George Papadopoulos, pursued Russia’s help in the campaign, interacted with a suspected Russian agent who promised compromising information about Clinton, and later lied to the FBI about his activities. Roger Stone, a longtime Republican operative, dropped hints during the campaign that he had advance knowledge of the release of material hacked from the Clinton campaign. As Trump was sewing up his party’s nomination in June 2016, a Russian lawyer offering information on Clinton was granted a meeting at Trump Tower with Trump’s eldest son, Donald Jr.; son-in-law, Jared Kushner; and campaign chairman, Paul Manafort. And a Justice Department lawyer told a judge that Manafort may have been a “back channel” between the campaign and Russians intent on meddling in the election.

3. Who is investigating?

Robert Mueller, a former Federal Bureau of Investigation director, was called back into service as special counsel to oversee the probe. He was appointed on May 17 by Rod Rosenstein, the deputy attorney general, who cited the “unique circumstances” of the case. Eight days before the appointment, Trump had fired the head of the FBI, James Comey, who’d been a key player in the investigation. Appointing Mueller was Rosenstein’s call because his boss, Attorney General Jeff Sessions, who was a top Trump adviser during the campaign, recused himself.

4. How did this all begin?

In April 2016, Democratic Party leaders called in a cybersecurity firm to look at suspicious software on their computers. The firm said it found digital footprints of hackers tied to the Russian government. The Democratic National Committee went public with the news and the suspicion of Russian involvement in June, just after Clinton clinched the party’s nomination for president, and just after WikiLeaks editor Julian Assange said his group had ”upcoming leaks in relation to Hillary Clinton.”

5. What were those leaks?

WikiLeaks released almost 20,000 emails from inside the Democratic National Committee that showed, among other things, how DNC staffers had favored Clinton during her primary campaign against Bernie Sanders -- prompting Debbie Wasserman Schultz to resign as DNC head. Later in the campaign, WikiLeaks released tens of thousands of emails from the Gmail account of John Podesta, Clinton’s campaign chairman. Clinton, looking back on her defeat, said the “WikiLeaks email dumps” had been “like Chinese water torture.”

6. And WikiLeaks got those emails from Russia?

That’s the allegation. The report by U.S. intelligence agencies says Russia’s General Staff Main Intelligence Directorate, or GRU, gave the material to WikiLeaks through an intermediary. (Assange has said the source of the hacked emails “is not the Russian government and it is not a state party,” though that doesn’t rule out the possibility that an intermediary was used.) Some of the emails also were released through the “persona” of a purported Romanian hacker, Guccifer 2.0, and a website, DCLeaks.com, both of which promoted the hacked information to certain journalists.

7. Which Trump aides are under scrutiny?

Potentially any who had contact with Russian representatives or intermediaries during the presidential campaign. That list includes Trump Jr., Kushner and Stone, plus:

• Michael Flynn, who lasted just 24 days as Trump’s first national security adviser. In the words of former acting Attorney General Sally Yates, Flynn “compromised” himself -- made himself vulnerable to being blackmailed -- by lying about the contents of a December 2016 phone call with Russia’s ambassador to the U.S., Sergey Kislyak. Flynn pleaded guilty to lying about that call to federal agents and has agreed to cooperate with investigators.

• Manafort, Trump’s onetime campaign chairman. He was charged on Oct. 27 with money laundering, conspiracy and tax charges in a 12-count indictment that says he used $18 million in laundered funds to support a “lavish lifestyle.” He received more than $17 million for his work with Ukraine’s pro-Russian Party of Regions in 2012-2013 and, according to corporate records, took as much as $52.8 million in loans from companies controlled by Russian billionaire Oleg Deripaska. He goes on trial on July 25.

• Carter Page, a U.S. energy consultant once listed by Trump as a foreign policy adviser, whose July 2016 visit to Moscow drew the FBI’s interest.

8. Is Trump himself being investigated?

Mueller appears interested in whether Trump obstructed justice by, among other actions, firing Comey as FBI director in May 2017; allegedly asking Comey, days earlier, to go easy on Flynn; and allegedly asking Comey for a pledge of loyalty. Then there’s Trump’s personal involvement in the drafting of a misleading statement that tried to spin the June 2016 Trump Tower meeting -- the one that included his son, son-in-law and a Russian lawyer -- as being about international adoptions. That’s not including any legal jeopardy Trump might face from the separate investigation of his lawyer and fixer, Michael Cohen.

9. Why is Mueller allowed to look beyond the Russia question?

The Justice Department’s May 17 order appointing Mueller instructs him to investigate “any links and/or coordination between the Russian government and individuals associated with the campaign,” as well as -- and this is key -- “any matters that arose or may arise directly from the investigation.” Trump and his lawyer, John Dowd, say that digging into matters beyond Russia and the 2016 election is out of bounds.

10. Does Trump acknowledge Russian meddling in the election?

He’s given mixed signals. He dismissed such reports during the campaign, theorizing that Democrats could just as easily have been hacked by “somebody sitting on their bed that weighs 400 pounds.” Since then, he’s called the concern about Russian involvement “fake news put out by the media,” a “ruse” and a “scam.” In November, he said he believed Putin was sincere in denying Russian meddling in the 2016 election. The next day, Trump said he stands with U.S. intelligence agencies on the matter.

• The latest indictment of Russians by Mueller’s team.

• A deep dive into Manafort’s lucrative Ukraine years.

• More on Manafort and that Russian oligarch.

• Why Mueller is one contestant Trump can’t easily fire.

• Here are Russia-backed Facebook ads you might have seen in 2016.

• QuickTake explainers on impeachment and obstruction of justice.

• Looking back: People, Politico and the BBC on the biggest revelations from hacked Clinton emails.

• There’s lots of evidence of collusion, Jonathan Chait writes in New York Magazine.

• A QuickTake explainer on cybercrime and cybersecurity.

• Remembering when Putin came up in that Clinton-Trump debate.

To contact the reporter on this story: Laurence Arnold in Washington at larnold4@bloomberg.net

To contact the editors responsible for this story: Leah Singer at lharrison@bloomberg.net, Larry Liebert, Anne Cronin

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