Robert Mueller’s sprawling 22-month probe into Russian election interference has failed to establish Donald Trump’s presidential campaign team conspired with Moscow to sway the 2016 election, but questions remain over the contents of the report, and the US president’s conduct since taking office.

William Barr, Mr Trump’s newly-installed attorney general, sent a four-page letter to Congress on Sunday outlining the contents of special counsel Mr Mueller’s report, which was submitted to the Justice Department on Friday.

According to the letter, Mr Mueller and his team did not find a direct link between Mr Trump’s campaign and Russia, but stopped short of ruling on whether Mr Trump obstructed justice.

Mr Mueller laid out evidence on “both sides” of the obstruction question, but, according to the letter, although it “does not conclude that the President committed a crime, it does not exonerate him”.

Mr Barr wrote he and deputy attorney general Rod Rosenstein - both Trump allies appointed by the president - themselves concluded there was insufficient evidence to charge the president with a crime.

Criminals who worked for Trump Show all 5 1 /5 Criminals who worked for Trump Criminals who worked for Trump Michael Cohen Former lawyer for Donald Trump was sentenced to three years in prison on counts involving evading income tax, false disclosure of the hush money paid to Stormy Daniels and another hush money charge Getty Criminals who worked for Trump Paul Manafort Former campaign manager for Trump Manafort was found guilty in February 2018 of five counts of tax fraud, two counts of bank fraud and one count of failure to disclose a foreign bank account. The crimes occurred prior to his appointment in Trump's campaign Getty Criminals who worked for Trump George Papadopoulos Former Trump campaign adviser Papadopoulos pleaded guilty to lying to the FBI in October 2017. He had lied about making contact with a professor who claimed that the Russians had dirt on Hillary Clinton. He was sentenced to 14 days in jail Getty Criminals who worked for Trump Michael Flynn Former White House National Security adviser Michael Flynn pleaded guilty to lying to the FBI in December 2017. He had lied about conversations that he had with the Russian ambassador to the US during Trump's Presidential campaign. He was not given prison time due to his "significant assistance" to the Mueller investigation Getty Criminals who worked for Trump Rick Gates Deputy chairman of Trump's presidential campaign Gates pleaded guilty to lying to the FBI in February 2018 AFP/Getty

Mr Trump declared the report provided “complete and total exoneration” and claimed the probe amounted to an “illegal takedown that failed”.

Mr Barr said he would have to consult with Mr Mueller and other US justice department officials before he can release more of the confidential report or any other information he gathered during the investigation.

But unless and until the full report is made, major questions will remain about Mr Mueller’s findings. Here are four of the biggest:

1. What evidence is there Mr Trump obstructed justice?

The letter highlights “a number of actions” Mr Mueller investigated as “potentially raising obstruction-of-justice concerns”, though Mr Barr fails to provide any detail.

Democrats were calling for the full release of the report even before they received Mr Barr’s letter, and the conspicuous lack of detail has only strengthened demands to make it public.

Mr Barr states Mr Mueller presented evidence “on both sides” of the obstruction question, but “ultimately determined not to make a traditional prosecutorial judgment”.

Unless the report is released, Congress and the public will remain in the dark about the incidents that caused Mr Mueller and his team “concerns”.

Donald Trump plays golf with Kid Rock at Trump International Golf Club in Florida

2. Collusion

Although Mr Barr says Mr Mueller “did not establish” that members of Mr Trump’s team conspired with the Russian government, the letter does not say what Mr Mueller learned that fell short of a crime about a broad range of Trump associates who had Russia-related contacts.

It also does not answer why several of those people lied to federal investigators or Congress during the Russia probe.

The report may shed further light on incidents such as Donald Trump Jr’s secret meeting with a Russian lawyer in 2016 to discuss getting “dirt” on Hillary Clinton, and former Trump adviser Roger Stone’s communications with WikiLeaks.

3. Lack of direct quoting of Mueller

Unlike previous independent counsels, there has so far been no disclosure of a summary provided by Mr Mueller himself, raising questions about Mr Barr’s interpretation of a report politicians and the public are yet to see.

Mr Barr’s summary includes only a handful of quotes lifted directly from Mr Mueller’s report; only one of which appears to be a sentence in full.

It's unclear what else is coming from Mr Barr, though he states in the letter that he is working to make more information public. He said he will be consulting with Mr Mueller to determine what else can be released.

But whatever is provided is unlikely to be enough for Democrats, who have said they want all of Mr Mueller's underlying evidence — including interviews and documents.

4. Is Mr Trump out of the woods?

It appears not. The US Constitution empowers Congress to remove a president from office for “high crimes and misdemeanors,” including obstruction of justice through a process of impeachment.

In an impeachment proceeding, lawmakers have broad leeway to define obstruction of justice and are not bound by Barr’s determination, legal experts said. The full report may make clear Mr Trump committed obstruction in the eyes of lawmakers.

Mr Trump also plays a central role in a separate case in New York, where prosecutors have implicated him in a crime.

They say the president directed his personal lawyer Michael Cohen to arrange illegal hush-money payments as a way to quash potential sex scandals during the campaign. New York prosecutors also are looking into Mr Trump's inaugural fund.

Congressional investigations also are swirling around the president. Democrats have launched a sweeping probe over Mr Trump that threatens to shadow the president through the 2020 election season.

And they are now demanding that Mr Barr should turn over Mr Mueller's confidential report and the underlying evidence he gathered in order for them to draw their own conclusions.