Donald Trump calls it “the Russian thing” and it is sending him on a slope to possible impeachment.

The “thing” is an accumulation of claims he has dark personal, financial and political connections with Russia which continued through the election campaign.

The President is in danger of charges he has interfered with the course of justice with heavy-handed interventions which continue to preoccupy his administration.

All to cover up the connections.

His future will depend on the deliberations of a US Senate judicial sub-committee on Russia, which is about to call some interesting witnesses and subpoena some fascinating evidence.

There also are calls for a storage inquiry with an independent prosecutor — who can’t be sacked by the President. The Trump grip on the presidency he won despite a hostile political establishment is close to being prised loose by that very establishment.

And they have what is at least circumstantial evidence to back the offensive. On Australia Day, January 26, the acting US Attorney-General Sally Yates went from her Washington office to the White House with what she considered an urgent warning.

She told the presidential legal adviser, White House counsel Donald McGahn, that national security adviser Michael Flynn had lied about his contacts with the Russians. Her advice was based on briefings from FBI Investigators.

Ms Yates feared the lies could make Mr Flynn vulnerable to Russian blackmail. She warned the President’s closest national security adviser could be a victim of what Moscow calls Kompromat — compromising material.

Within four days she was fired by President Trump, ending 27 years with the Justice Department. And on May 9 James Comey was sacked as FBI director.

The public reason for Ms Yates going was her legal opinion opposing President Trump’s executive order banning immigration from seven Muslim countries. She said it was unconstitutional because it was based on religious discrimination. This was a rebuff to Mr Trump’s campaign promise.

Mr Comey was forced out because, the White House said, he had failed to have charges laid against Democrat presidential candidate Hillary Clinton.

During the campaign Mr Trump led crowd chants of “Lock her up” and vowed Ms Clinton would be jailed. They were the official reasons, but underlying the ruthless pruning of these top public servants was the lingering taint of Michael Flynn.

Sally Yates believes that was at least part of the motive for her sacking, and the release today of a memo written by Mr Comey indicates he also thinks “this Russian thing” saw him booted. Mike Flynn was sacked on February 13 for misleading Vice-President Mike spence on meetings with a Russian diplomat. He then asked about the prospect of immunity were he to tell all to any inquiry.

The next day, February 14, Mr Comey attended a White House meeting at which, his memo written hours later reportedly says, Mr Trump cleared the room and asked him for soft treatment of Mr Flynn.

“I hope you can see your way clear to letting this go, to letting Flynn go,” the President is quoted as saying.

“He is a good guy. I hope you can let this go,” the memo records him saying.

Trump critics see this as an attempt to shut down the FBI inquiry. The White House has denied it totally and said the President was putting in a good word for a former general “who had served and protected our country”.

But two days after punting the FBI chief, Mr Trump tweeted: “James Comey better hope that there are no ‘tapes’ of our conversations before he starts leaking to the press.”

James Comey better hope that there are no "tapes" of our conversations before he starts leaking to the press! — Donald J. Trump (@realDonaldTrump) May 12, 2017

That looked very like a pre-emptive strike. And it didn’t work. There now is a keenness for the Senate sub-committee to call on Mr Comey to testify and for production of his memoes, and the Trump tapes, should they exist.

It’s always the cover-up, not the crime. That’s one lesson from Watergate, and President Trump is being reminded of this, perhaps too late.