There is one week to go and all is confusion. Next Friday Donald Trump will take the oath of office and be sworn in as president of the United States. But still no one has the first clue how to handle what’s coming. Politicians, journalists and diplomats, in the US and around the world, are searching for guidance, desperately flicking through the pages of the rulebook, a manual full of past precedents and norms that they have spent their careers mastering – but that Trump burned and shredded months ago.

In normal times, even those few parts of this week’s “dirty dossier” affair that are firmly established would be enough to undo an incoming president. Put aside the lurid details of what went on in Moscow hotel rooms. Assume they’re untrue. Focus instead on the fact that the US Department of Justice sought and eventually gained secret court warrants to investigate two Russian banks and their links with a series of Trump associates.

Remember how much damage it did to Hillary Clinton for the FBI to be looking (again) at her use of a private email server. Regardless of what they found – nothing, as it happens – the mere fact that she was under investigation wounded her badly, perhaps even denying her the presidency. Yet now we know that federal investigators were keen to probe Team Trump not over its email habits, but something much more serious: possible links with a hostile foreign power.

We’ve learned too that the dossier included a claim of secret meetings between Trump aides and Russian officials. Now, that claim has not been proved and could of course turn out to be, as Trump insists, “garbage”. But it comes from a document deemed sufficiently credible by US intelligence agencies that they briefed both President Obama and Trump on its contents.

In the same vein, and in an astonishing development, the Israeli press has reported that its country’s intelligence officials have been advised by their US counterparts not to share intel with the Trump administration, lest that information find its way to Moscow, and from there to Tehran. In effect those US spooks have said that their own incoming president cannot be trusted with secrets, because Vladimir Putin has “leverages of pressure” over him.

In normal circumstances just the fact of these investigations would be enough to hobble a president. But nothing about these circumstances is normal. Indeed, the lesson of the past year is that what would destroy a normal politician often leaves barely a scratch on Trump. Sometimes it even makes him stronger.

Israel has reportedly been advised by US intelligence not to share intel with the Trump administration

In this particular case, there is no guarantee, in a clash between the intelligence agencies and media, on the one hand, and Putin on the other, that Trump’s supporters wouldn’t side with Putin. After all, a poll last month showed Republicans with a favourable view of the Russian leader outnumbered those who approved of Obama by 37% to 17%.

If Trump turns his full rage on the spooks – and he has barely got started – reminding Americans of the debacle of the Iraqi weapons of mass destruction that never were, conveniently omitting to mention the pressure the Bush administration put on the spies to produce the answers it wanted to hear – who’s to say that’s a battle he won’t win?

The price will be an American public who won’t believe the intelligence services even when they warn of genuine dangers to national security – but Trump won’t care about that. He does not mind trampling over the republic’s key institutions, as long as it helps him.

The mistake is to project on to Trump the standards that would normally apply. Take this week’s parallel drama, as several of his nominees came before the senate to have their appointments confirmed. They all offered sweet words of reassurance: the would-be attorney general insisting he was no racist; the prospective secretary of state avowing that he was no patsy to Putin. Official Washington seized on these morsels of comfort, especially when Trump tweeted an apparent admission that his senior team were at odds with him on several core issues: “I want them to be themselves and express their own thoughts, not mine!”

But what if such licensed independence is all for show? Maybe Trump has no plan to use these cabinet members for anything but window dressing. On foreign policy, Rex Tillerson could turn out to be a glorified ambassador, says Robin Niblett, the director of Chatham House. Real decision-making power might reside with Trump, son-in-law Jared Kushner, Breitbart founder Steve Bannon, and firebreathing national security adviser Mike Flynn. That would fit Trump’s style, says Niblett, with “Power concentrated ever closer around the chief executive.”

Or maybe Washington was simply looking through the old lens? Surely it is just as possible that Trump’s team gave his nominees permission to say whatever they had to say to get confirmed, true or false. For Trump, consistency and truth are for losers. Much simpler to lie, if that’s what gets results. So Tillerson didn’t need to get tangled up in a long debate over US policy on Russia: he just had to say that he and Trump had never even discussed it, implausible as that might sound. Job done.

For critics, this poses a conundrum. Too often they deal with Trump as if he is a normal politician, constrained by the usual conventions, including embarrassment at being caught in a lie. But Trump is not a normal politician. He has no shame. While most politicians blush if exposed as inconsistent, let alone dishonest, Trump is unembarrassable. Even Nixon tried to squirm and wriggle his way into a sentence that could be parsed as truth. Trump, hailed as the God Emperor by his supporters, simply attacks whichever little boy dares say he’s wearing no clothes – before going on to accuse the child of being a “failing pile of garbage”.

There is no precedent to guide the media or policymakers, because there has been no US president remotely comparable to Trump. Sticking to the old rulebook, now charred and in tatters, will be a grave mistake. Nowhere more so than Britain.

London’s default setting since 1945 has been to be as close to Washington as humanly possible. That’s what the manual, handed to every diplomat and every new occupant of No 10, demands. Sure enough, Theresa May is following it – dispatching her joint chiefs of staff, rather than the UK ambassador, to Trump Tower to beg for an early meeting between the two leaders, amid all the familiarly needy, unrequited talk of a “special relationship”.

This is certainly what you’d expect of a British prime minister if a normal American president were about to take over on 20 January. But May has not sufficiently absorbed that Trump is an aberration, and therefore the usual rules should not automatically apply. (Angela Merkel has been much more wary.)

Theresa May is repeating the same mistake so fatefully made by Tony Blair in 2001

Instead, May is repeating the same mistake so fatefully made by Tony Blair in 2001. He thought he should be as close to George W Bush as he’d been to Bill Clinton, failing to appreciate that the two men were entirely different, that Bush was surrounded by ideological obsessives who were bent on war with Iraq from the very start. May is being similarly undiscriminating. In her post-Brexit longing for friends and trading partners, she is getting ready to cosy up to a man who makes Bush look like Abraham Lincoln. It may prove to be her costliest error.

But you can see why it’s happened. She and her officials know no other way to operate. Along with everyone else, they keep clinging to the hope that Trump is about to transform himself into a politician they can recognise and understand.

But he hasn’t and he won’t. They, and we, need to stop deluding ourselves – and work out how to deal with Trump just the way he is.