With explosive revelations emerging, the probe into Moscow’s ‘meddling’ is heating up.

Subpoenas are flying, a special prosecutor is taking the reins, and explosive revelations hit the press almost daily: the investigation into possible collusion between President Donald Trump’s campaign and Russia is heating up.

With Mr. Trump reported to have retained a personal lawyer to represent him, here is where the sprawling probe into alleged Russian interference in the 2016 election stands.

What US intelligence knows

Top intelligence officials announced in January their belief that Russia’s Vladimir Putin directed a plot to hurt Democrat Hillary Clinton and boost the election chances of her rival Mr. Trump.

This week, former Central Intelligence Agency (CIA) director John Brennan revealed that intelligence chiefs had been looking into suspicious contacts between Trump campaign associates and Russian officials since mid-2016.

He also made clear the Federal Bureau of Investigation (FBI) probe launched in July last year into Russian hacking of Democratic Party communications, was already pursuing possible Trump campaign collusion with Moscow.

Those suspicions lingered but proof was lacking. When Mr. Brennan left office in January, he had said he had “unresolved questions in my mind as to whether or not the Russians had been successful in getting US persons involved in the campaign or not to work on their behalf.”

Is Trump in trouble?

Mr. Trump rejects the suggestion his team colluded with Moscow as a “witch-hunt,” and so far there is little more than circumstantial evidence of any personal links between the US President and Russia, most of which involves his family’s real estate businesses.

His biggest problem stems from his repeated efforts to persuade senior politicians, justice and intelligence officials to help push back against the probe, and his firing of James Comey as FBI director on May 9. Those actions have brought accusations that he is obstructing the investigation.

Obstruction of justice was one of the key charges levied against both President Richard Nixon, in 1974 in the Watergate case, and Bill Clinton in his 1998 impeachment in connection with the Monica Lewinsky scandal.

Mr. Trump’s unwillingness to criticise Moscow has further stoked suspicions. It didn’t help when he invited Russian Foreign Minister Sergei Lavrov into the Oval Office in early May — and reportedly divulged to him top secret intelligence on the Islamic State group.

Flynn’s flip-flops

Number one in the hot seat is Michael Flynn, Mr. Trump’s advisor on national security in the campaign and, for four weeks, in the White House. Mr. Flynn’s dealings with Russians raised concerns in the Justice Department that he could have been compromised by Russian intelligence — and been vulnerable to blackmail. That is one reason he was forced out of the White House in February.

Mr. Flynn’s misleading statements about money he received from Russian and Turkish government-related bodies, and his frequent contacts with Russia’s US Ambassador after the election, are being examined by the Justice Department, Congress, and the Pentagon.

This week Mr. Flynn refused to comply with a Senate Intelligence Committee subpoena for documents, claiming his constitutional right against self-incrimination. But he also appeared ready to testify in exchange for immunity.

“General Flynn certainly has a story to tell, and he very much wants to tell it,” his lawyer has said.

Several other campaign aides with links to Russia, including one-time campaign chairman Paul Manafort, are also being examined. And recent press reports have said a grand jury is seeking information from an unnamed current White House advisor.

Comey may reveal Trump ‘pressure’

All eyes are on Mr. Comey, who is expected to testify to Congress in coming weeks, making his first public comments since he was fired. He could detail Mr. Trump’s alleged pressure on him to pull back the probe, as well as shed light on how strong the evidence is of alleged collusion.

Former FBI director Robert Mueller is currently taking over the agency’s investigation after being appointed as a special prosecutor, insulated from political pressure to pursue all leads. His work could take months.

In the meantime, the two key panels in the Congress investigating the Russia affair, the House and Senate intelligence committees, continue to collect their own data. Others are also joining in. On Wednesday the Financial Services Committee demanded Deutsche Bank turn over records on its banking relationship with Mr. Trump.