Is it “utter nonsense” or “explosive” allegations that have circulated at the highest levels of the American government? Or, quite conceivably, both?

If it is true that the Russians really have in their possession a dossier of damaging details about Donald Trump, and it is also true that they have sought to use this in effect to blackmail the candidate and now President-elect, then that is certainly political dynamite. It fuels the suspicion – though, again, does not prove it – that Mr Trump’s conciliatory attitude to Vladimir Putin is not solely driven by consideration of the American national interest. It suggests that the US presidential election of 2016 was not only hacked by the Russian secret service – a widespread and plausible claim – but that it was in effect run by the Russians for the benefit of the Russian government.

All this – far away from anything approaching proven reality yet – would be deeply, and possibly fatally, damaging to Mr Trump. If, true to form, he continues to deny everything, to bluster and brazen it all out, and to reply on the inevitable doubts that inevitably surround even well-founded intelligence, then it would still leave his presidency dead in the Potomac almost before it has begun.

Donald Trump in angry exchange with CNN reporter after President-elect refuses question

His nominal Republican allies in Congress, let alone bitterly resentful Democrats, would simply refuse to cooperate with him on any but the most basic levels of governance. He would be able to pursue no initiatives and would face the constant threat of impeachment and political alienation. Even a man of Mr Trump’s disposition might not wish to endure four years of that – particularly if it became demonstrably good for America that he stood down before any impeachment proceedings are launched. As with Richard Nixon before him, if it is obvious that he no longer has a sufficient base of support in the Congress to continue in office, then his position will become untenable.

That is a long way away, if it is a realistic scenario at all. Yet even if there is little truth in the rumours, the damage they are already doing to confidence in the office of the presidency is obvious. Hardly less grievous is the damage they are inflicting on the US intelligence agencies – damage that is in effect being channelled by Mr Trump and his splenetic outbursts via Twitter.

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No stranger to strange and irrational tweets, Mr Trump is now demonstrating the truly awesome power of one powerful man left alone with a smartphone. Already sceptical about the agencies, he has publicly ridiculed their briefings on Russian influence on the election and their effectiveness. Mr Trump seems neither to know nor care that they are supposed to be independent agencies, a part of the federal executive but insulated from direct direction and influence by the President himself (as was made apparent in the Watergate affair four decades ago). He seems to have entirely forgotten the baleful role the FBI played in stymying Hillary Clinton’s election prospects so late in the campaign, when they brought up once again her private email accounts.