So now we know that President Trump and his press secretary are strict followers of Marx – not Karl, but Groucho.

For it was Groucho Marx’s character – impersonated for that scene by brother Chico – who asked, in the 1933 classic Duck Soup, “Who are you going to believe, me or your own eyes?” In his first appearance at the podium as White House press secretary on Saturday, Sean Spicer adhered to that same Marxist doctrine by demanding that the media ignore the clear evidence of their own eyes, as well as photographs and video footage, and instead believe Trump’s claim that he had drawn record-breaking crowds to his inauguration ceremony the previous day. Or to be precise, “the largest audience to ever witness the inauguration – period. Both in person and around the globe.”

Every possible data point – TV ratings, stats for use of the Washington Metro system, expert crowd analysis – confirms that to be false. So why would Spicer and his boss launch a new administration with such an obvious, disprovable falsehood?

Its immediate effect has been to turn Spicer into a laughing stock, a White House counterpart to the spokesman for Saddam Hussein, forever known as Comical Ali, who famously insisted to reporters that Baghdad was safely in the dictator’s hands even as live pictures showed the city had been overrun. The social media memes have been instant, typified by an imaginary Spicer briefing that the passengers of the Titanic had a fabulous voyage and cannot wait to re-board the ship for its return voyage to Southampton.

Earlier this month, Spicer himself said that “I’ve never lied … if you lose the respect and trust of the press corp, you’ve got nothing.” It’s not as if he was not aware of the risks. So why do it?

The first and most obvious explanation is that Spicer was simply following the orders of his boss, who made a similar brag to the agents of the CIA when he visited their Langley headquarters on Saturday. The clearest sign that Trump has not made the transition from reality TV star to head of government is his ongoing obsession with TV ratings. On Sunday morning he was at it again, tweeting about his viewing figures. And his account of his CIA visit could not help but include a boast that he had a “packed house” that gave him “long standing ovations”.

The larger point is that Spicer wanted to issue a declaration of war against the press, because that is what Trump intends to pursue. The media has become his defining enemy, taking the place of Hillary Clinton as the glue that might bind his supporters. Whatever his own failings to come, he can always get the base riled up in their hatred of the mainstream media. As Evan McMullin, the conservative who ran against Trump as an independent, put it, these repeated attacks on the press are “intended to destroy the media’s ability to hold him accountable”.

We should also listen closely to those commentators raised under authoritarian regimes. They note that leaders in that mould often spread falsehoods, or at least try to make facts seems hazy and unknowable. If a chunk of the population are not sure what’s true and what’s not, their willingness to fight back is weakened. They are more likely to greet each new and deteriorating development with a shrug of confusion: “Who knows?”

More darkly still, the authoritarian regards telling the population lies to be a test of strength. The Trump White House will now watch closely to see who repeats Spicer’s falsehoods without protest and who objects. Among the media, the former will be rewarded and the latter punished.

But it’s even more basic than that. Authoritarian strongmen crave control. If they can control what you believe – even make you believe that black is white and night is day – then their power over you is total. Not for nothing did George Orwell’s 1984 have the omnipotent Party persuade Winston Smith that if a Party official said he was holding up five fingers, then he really was holding up five – even if Smith could only see four.

When a press secretary tells you a crowd reached all the way to the Washington Monument, even when every witness and photograph says otherwise, this tells you what game the Trump administration intends to play. Note the way Spicer took no questions and described the reception given to Trump by those CIA employees as “ecstatic”. This is a style of press briefing that is less Washington than Pyongyang.

The press now has a choice to make. It can pretend that this approach is normal and cover this White House in the normal way. Or it can change its approach. To its great credit, CNN did not broadcast the Spicer briefing live but showed extracts afterwards, together with context and fact-checking. That seems a wise precedent. Either way, Donald Trump has signalled – yet again – that he is ready to break the norms associated with democratic societies. And he’s done it on day one.