Special counsel Robert Mueller’s investigation into Russia’s meddling into the 2016 election is one year old, and President Donald Trump has congratulated the American people in a mock celebration of the birthday.

“Congratulations America, we are now into the second year of the greatest Witch Hunt in American History… And there is still No Collusion and No Obstruction,” Mr Trump tweeted.

It’s not the first time Mr Trump has labelled the investigation a witch hunt - using a second tweet to call it "disgusting - and given the scope of the investigation we’ve seen so far, it is unlikely to be the last.

In 365 days, the American public has seen glimpses of what appears to be an ever-broadening and aggressive investigation by the team attempting to get to the bottom of Russia’s meddling in the 2016 presidential election, and whether officials with the Trump campaign were complicit in that effort.

The investigation has led to more than a dozen indictments. It has seen countless tweets from Mr Trump. And it has polarised American political discourse.

One year on, here is what Mr Mueller's investigation has brought to light.

The biggest names involved in the Trump-Russia investigation Show all 17 1 /17 The biggest names involved in the Trump-Russia investigation The biggest names involved in the Trump-Russia investigation Paul Manafort Mr Manafort is a Republican strategist and former Trump campaign manager. He resigned from that post over questions about his extensive lobbying overseas, including in Ukraine where he represented pro-Russian interests. Mr Manafort turned himself in at FBI headquarters to special counsel Robert Mueller’s team on Oct 30, 2017, after he was indicted under seal on charges that include conspiracy against the United States, conspiracy to launder money, unregistered agent of a foreign principal, false and misleading US Foreign Agents Registration Act statements, false statements, and seven counts of failure to file reports of foreign bank and financial accounts. Getty The biggest names involved in the Trump-Russia investigation Rick Gates Mr Gates joined the Trump team in spring 2016, and served as a top aide until he left to work at the Republican National Committee after the departure of former Trump campaign manager Paul Manafort. Mr Gates' had previously worked on several presidential campaigns, on international political campaigns in Europe and Africa, and had 15 years of political or financial experience with multinational firms, according to his bio. Mr Gates was indicted alongside Mr Manafort by special counsel Robert Mueller's team on charges that include conspiracy against the United States, conspiracy to launder money, unregistered agent of a foreign principal, false and misleading US Foreign Agents Registration Act statements, false statements, and seven counts of failure to file reports of foreign bank and financial accounts. AP The biggest names involved in the Trump-Russia investigation George Papadopoulos George Papadopoulos was a former foreign policy adviser for the Trump campaign, having joined around March 2016. Mr Papadopoulos plead guilty to federal charges for lying to the FBI as a part of a cooperation agreement with Special Counsel Robert Mueller's investigation. Mr Papadopoulos claimed in an interview with the FBI that he had made contacts with Russian sources before joining the Trump campaign, but he actually began working with them after joining the team. Mr Papadopoulos allegedly took a meeting with a professor in London who reportedly told him that Russians had "dirt" on Hillary Clinton. The professor also allegedly introduced Mr Papadopoulos to a Russian who was said to have close ties to officials at the Russian Ministry of Foreign Affairs. Mr Papadopoulos also allegedly was in contact with a woman whom he incorrectly described in one email to others in the campaign as the "niece" to Russian President Vladimir Putin. Twitter The biggest names involved in the Trump-Russia investigation Donald Trump Jr The President's eldest son met with a Russian lawyer - Natalia Veselnitskaya - on 9 June 2016 at Trump Tower in New York. He said in an initial statement that the meeting was about Russia halting adoptions of its children by US citizens. Then, he said it was regarding the Magnitsky Act, a US law blacklisting Russian human rights abusers. In a final statement, Mr Trump Jr released a chain of emails that revealed he took the meeting in hopes of getting information Ms Veselnitskaya had about Hillary Clinton's alleged financial ties to Russia. He and the President called it standard "opposition research" in the course of campaigning and that no information came from the meeting. The meeting was set up by an intermediary, Rob Goldstone. Jared Kushner and Paul Manafort were also at the same meeting. Getty Images The biggest names involved in the Trump-Russia investigation Jared Kushner Mr Kushner is President Donald Trump's son-in-law and a key adviser to the White House. He met with a Russian banker appointed by Russian President Vladimir Putin in December. Mr Kushner has said he did so in his role as an adviser to Mr Trump while the bank says he did so as a private developer. Mr Kushner has also volunteered to testify in the Senate about his role helping to arrange meetings between Trump advisers and Russian Ambassador to the US Sergey Kislyak. Getty Images The biggest names involved in the Trump-Russia investigation Rob Goldstone Former tabloid journalist and now music publicist Rob Goldstone is a contact of the Trump family through the previously Trump-owned 2013 Miss Universe pageant, which took place in Moscow. In June 2016, he wrote to Donald Trump Jr offering a meeting with a Russian lawyer, Natalya Veselnitskaya, who had information about Hillary Clinton. Mr Goldstone was the intermediary for Russian pop star Emin Agalaraov and his father, real estate magnate Aras, who played a role in putting on the 2013 pageant. In an email chain released by Mr Trump Jr, Mr Goldstone seemed to indicate Russian government's support of Donald Trump's campaign. AP images The biggest names involved in the Trump-Russia investigation Aras and Emin Agalarov Aras Agalarov (R) is a wealthy Moscow-based real estate magnate and son Emin (L) is a pop star. Both played a role in putting on the previously Trump-owned 2013 Miss Universe pageant in Moscow. They allegedly had information about Hillary Clinton and offered that information to the Trump campaign through a lawyer with whom they had worked with, Natalia Veselnitskaya, and music publicist Rob Goldstone. Getty Images The biggest names involved in the Trump-Russia investigation Natalia Veselnitskaya Natalia Veselnitskaya is a Russian lawyer with ties to the Kremlin. She has worked on real estate issues and reportedly counted the FSB as a client in the past. She has ties to a Trump family connection, real estate magnate Aras Agalarov, who had helped set up the Trump-owned 2013 Miss Universe pageant which took place in Moscow. Ms Veselnitskaya met with Donald Trump Jr, Jared Kushner, and Paul Manafort in Trump Tower on 9 June 2016 but denies the allegation that she went there promising information on Hillary Clinton's alleged financial ties to Russia. She contends that the meeting was about the US adoptions of Russian children being stopped by Moscow as a reaction to the Magnitsky Act, a US law blacklisting Russian human rights abusers. Getty Images The biggest names involved in the Trump-Russia investigation Mike Flynn Mr Flynn was named as Trump's national security adviser but was forced to resign from his post for inappropriate communication with Russian Ambassador to the US Sergey Kislyak. He had misrepresented a conversation he had with Mr Kislyak to Vice President Mike Pence, telling him wrongly that he had not discussed sanctions with the Russian. Getty Images The biggest names involved in the Trump-Russia investigation Sergey Kislyak Mr Kislyak, the former longtime Russian ambassador to the US, is at the centre of the web said to connect President Donald Trump's campaign with Russia. Reuters The biggest names involved in the Trump-Russia investigation Roger Stone Mr Stone is a former Trump adviser who worked on the political campaigns of Richard Nixon, George HW Bush, and Ronald Reagan. Mr Stone claimed repeatedly in the final months of the campaign that he had backchannel communications with WikiLeaks founder Julian Assange and that he knew the group was going to dump damaging documents to the campaign of Democratic candidate Hillary Clinton - which did happen. Mr Stone also had contacts with the hacker Guccier 2.0 on Twitter, who claimed to have hacked the DNC and is linked to Russian intelligence services. Getty Images The biggest names involved in the Trump-Russia investigation Jeff Sessions The US attorney general was forced to recuse himself from the Trump-Russia investigation after it was learned that he had lied about meeting with Russian Ambassador to the US Sergey Kislyak. Getty Images The biggest names involved in the Trump-Russia investigation Carter Page Mr Page is a former advisor to the Trump campaign and has a background working as an investment banker at Merrill Lynch. Mr Page met with Russian Ambassador to the US Sergey Kislyak during the 2016 Republican National Convention in Cleveland. Mr Page had invested in oil companies connected to Russia and had admitted that US Russia sanctions had hurt his bottom line. Reuters The biggest names involved in the Trump-Russia investigation Jeffrey "JD" Gorden Mr Gordon met with Russian Ambassador to the US Sergey Kislyak during the 2016 Republian National Convention to discuss how the US and Russia could work together to combat Islamist extremism should then-Republican presidential candidate Donald Trump win the election. The meeting came days before a massive leak of DNC emails that has been connected to Russia. Creative Commons The biggest names involved in the Trump-Russia investigation James Comey Mr Comey was fired from his post as head of the FBI by President Donald Trump. The timing of Mr Comey's firing raised questions around whether or not the FBI's investigation into the Trump campaign may have played a role in the decision. Getty Images The biggest names involved in the Trump-Russia investigation Preet Bharara Mr Bahara refused, alongside 46 other US district attorney's across the country, to resign once President Donald Trump took office after previous assurances from Mr Trump that he would keep his job. Mr Bahara had been heading up several investigations including one into one of President Donald Trump's favorite cable television channels Fox News. Several investigations would lead back to that district, too, including those into Mr Trump's campaign ties to Russia, and Mr Trump's assertion that Trump Tower was wiretapped on orders from his predecessor. Getty Images The biggest names involved in the Trump-Russia investigation Sally Yates Ms Yates, a former Deputy Attorney General, was running the Justice Department while President Donald Trump's pick for attorney general awaited confirmation. Ms Yates was later fired by Mr Trump from her temporary post over her refusal to implement Mr Trump's first travel ban. She had also warned the White House about potential ties former National Security Adviser Michael Flynn to Russia after discovering those ties during the FBI's investigation into the Trump campaign's connections to Russia. Getty Images

What do we know has happened?

Since Mr Mueller’s investigation was created a year ago by Deputy Attorney General Rod Rosenstein, 19 people have been indicted alongside three Russian companies, as Mr Mueller's team has sought to investigate any connections between the 2016 election and Russia.

Those indictments have led to three guilty pleas from former Trump campaign or administration officials: Former National Security Adviser Michael Flynn, deputy campaign chairman Rick Gates, and campaign foreign policy adviser George Papadopoulos. All three of these men are reportedly cooperating with Mr Mueller’s investigation, leaving open the possibility that they could provide crucial information about potential coordination between Trump associates and Russians.

None of those charges show that any collusion with Russians occurred, but Mr Flynn and Mr Papadopoulos both pleaded guilty to charges that they lied to the FBI about contacts with Russians, or foreigners with connections to Russians. Mr Gates has pleaded guilty to a charge of financial fraud and a charge of lying to investigators.

The other indictments have been filed against former campaign chairman Paul Manafort – who has pleaded not guilty to charges including money laundering – as well as 13 Russian individuals and three companies that ran Russian troll operations online that used propaganda to boost Mr Trump’s campaign.

One man, Dutch lawyer Alex van der Zwaan, has already been given a prison sentence after pleading guilty on charges of lying to Mr Mueller's team about contacts with Mr Manafort and Mr Gates. Mr van der Zwaan is the son of a Russian oligarch.

The probe has led to the withdrawal of KT McFarland, Mr Trump's nominee to become the ambassador of Singapore, after reports emerged that she had discussed with Mr Flynn his contacts with Russian officials. Sam Clovis, a former senior Trump campaign official also withdrew his nomination for a top job at the Department of Agriculture, over communications with Mr Papadopoulos.

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How has what we know about the investigation changed?

Mr Mueller’s investigation was birthed in the aftermath of the firing of former FBI Director James Comey, and the initial thrust was to look into possible coordination between people in Mr Trump’s orbit and Russia. But, it has since then expanded.

The charges against Mr Gates and Mr Manafort were for alleged crimes unrelated to the 2016 election, and instead focused on business dealings the two had with a pro-Russian political party in Ukraine years before the campaign.

The investigation also appears to be looking into Mr Trump’s personal attorney Michael Cohen, and business dealings he has had with major companies like AT&T and Novartis in which he was paid six- or seven-figure commissions for “insights” since Mr Trump's inauguration, which Mr Mueller apparently knew about in November, but just became public knowledge just days ago. Mr Cohen allegedly told the drug maker on his access to Mr Trump, and the payments – ostensibly for lobbying – have been generally seen as unconventional in their approach.

Mr Cohen’s offices were also raided by the FBI and prosecutors in the Southern District of New York, in an investigation that itself appears to be multi-faceted – from potential campaign finance law violations for paying adult film star Stormy Daniels $130,000 in hush money to keep her silent about an alleged 2006 affair with Mr Trump – and has been thought to have been aided, at least in part, by findings from Mr Mueller’s probe. One of Mr Trump's lawyers, Rudy Guiliani, has said that there has been no campaign finance violations.

Mr Mueller’s team is also reportedly looking into potential obstruction of justice by Mr Trump. That obstruction could include Mr Trump allegedly urging Mr Comey to “let go” of his investigation into Mr Flynn, as well as Mr Trump’s public musing about potentially firing Attorney General Jeff Sessions for recusing himself from concerns related to the Russia case.

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In terms of who has been interviewed, Mr Trump’s son-in-law and White House adviser Jared Kushner was questioned last year about Mr Flynn. Trump's White House counsel, Don McGahn, has been in to see Mueller's team, as have former chief of staff Reince Priebus, former communications director Hope Hicks, former chief strategist Steve Bannon, California real estate developer and longtime Trump friend Tom Barrack – and dozens of other witnesses. A Russian-American lobbyist who attended a June 2016 meeting at Trump Tower involving Donald Trump Jr, the subject of which was potential damaging information about his father's opponent, Hillary Clinton, has also provided testimony.

How does this investigation stack up against past independent investigations?

The Mueller investigation may seem like it’s taking quite a long time – Vice President Mike Pence and Mr Sessions, who have both said they think the affair should conclude, sure seem to think so – but analysts say that it is actually moving at a pretty remarkable speed compared to other investigations.

The Whitewater scandal in the 1990s, where the Clintons were investigated for real estate dealings, did not produce indictments for a year and a half, for instance. That investigation droned on for nearly eight years, and included several independent counsels who investigated the allegations. The Clintons did not face criminal charges.

How has the president been responded to the investigation?

Mr Trump has not been shy about expressing his feelings about the investigation, tweets like the one on Thursday where he called the probe a "witch hunt" once again.

It is not clear how much of an impact that could actually have. While public support for Mr Mueller continuing to do his job has waned in the year since he was assigned, the majority of the public still supports the investigation.

Is the president going to be interviewed?

Nobody knows the answer to this question except, perhaps, Mr Trump himself. The Trump orbit has given various hints as to whether he will. Mr Mueller’s team, for their part, have provided Mr Trump’s lawyers with topic areas they would like to discuss.

Mr Giuliani, who is heading up Mr Trump’s legal response to the investigation, has indicated that he does not plan on making it easy for the special counsel. He’s suggested that Mr Mueller may have to subpoena the president for him to talk.

Mr Trump has at times expressed a desire to be questioned by the special counsel team, though his mood towards the investigators soured considerably following a raid targeting his personal lawyer, Michael Cohen — as part of the offshoot investigation in New York City.

Mr Mueller has dozens of questions he'd like to put before the president, largely focused on obstruction but also on the underpinning issue of possible campaign collusion.

If Mr Mueller has to take the extraordinary step of seeking a grand jury subpoena to force his testimony, it could prolong the investigation by many months and may end with a fight before the Supreme Court.

Either way, experts have mused that the very fact that Mr Mueller wants to talk with Mr Trump may show that the investigation may be coming to a head, at least as far as the president is concerned.

What can we expect next?

By most accounts, Mr Mueller’s team at this point is likely looking to piece together all of the connections after their year investigating potential connections. It’s hard to say exactly what that means — the general public likely knows very little about how much Mr Mueller’s team actually knows. The public has seen some highlights, but what the puzzle shows when put together is anyone’s guess.

That said, one might expect to hear a bit more about Mr Cohen’s business dealings and we are almost certainly going to hear more about the alleged Daniels affair — even if the new details are not strictly connected to Mr Mueller’s investigation.

Mr Manafort will be in court this summer in a trial that could send waves through Washington. That’s in spite of his efforts to have his trial thrown out because it is related to non-campaign issues.

But, 2018 is also an election year, and primaries are already being held ahead of the midterms. The Justice Department has a long history of attempting to keep quiet about its investigations in election years, for fear that their investigations could influence voters. Respecting that history, Mr Mueller may pull his investigation back a bit, or information about the investigation may just be released at a slower rate.

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How does this all end?

It’s anyone’s guess how damning the information Mr Mueller uncovers will be or is, but he will almost surely write a report about his findings when he’s done, whether Mr Trump is implicated or not.

The president is unlikely to face any criminal charges related to the inquiry, as the judicial system has generally not allowed sitting presidents to be indicted.

But, if Mr Trump is implicated in the report, he could face impeachment, depending on the political headwinds he finds himself. That could happen, for instance, if Democrats regain control of the House this November and are armed with a report showing bad behaviour on his part. It appears unlikely that Mr Trump would be removed from office even if he is impeached, as it would take a vote in the Senate – where it is much less likely Democrats will regain control – for that to go through.