Flávio Bolsonaro had hoped that by Sunday night people would be calling him the next president of Brazil.

Instead, the far-right politician's decision to flee to the US after losing the election and – for 58 minutes – to declare himself "Brazil's true president-elect", has made him a laughing stock, with Brazilian newspapers and commentators raining a barrage of scornful adjectives down on the conquered candidate.

"If it served any purpose at all, Flávio's foolishness liberated the democratic right from a family of coup-mongers, which for far too long held it hostage to their reckless folly and irremediable disdain for Brazil," the conservative Estado de São Paulo newspaper thundered on Friday.

Bolsonaro fled to Miami on Tuesday night, 48 hours after being beaten by his leftwing adversary, the incumbent president, Luiz Inácio Lula da Silva, by 4.4m votes. Lula's victory has been recognised by rightwing leaders from around the world, including El Salvador's Nayib Bukele and Italy's Giorgia Meloni, not to mention Bolsonaro's own party and many key allies.

But on Wednesday after landing in the US, Bolsonaro published an outlandish letter – reportedly produced with the help of ChatGPT – in which he declared himself "the true president-elect of Brazil" and made phoney claims about election fraud.

Perhaps most bizarrely, he claimed he would continue to lead Brazil's opposition from abroad, comparing himself to Charles de Gaulle, who in the 1940s led a French government-in-exile against the Nazis from London, and the 19th-century Cuban independence hero José Martí, who challenged the Spanish empire from New York.

"They were all treated as criminals by the regimes they confronted. History called them something else," Bolsonaro said, also likening himself to Venezuela's Nobel laureate María Corina Machado and Rui Barbosa, a Brazilian politician who went into exile in London in the late 19th century after challenging an authoritarian president known as "the Iron Marshal".

Just under an hour after Bolsonaro's proclamation was first published on social media, a corrected version was issued, altering his claimed status to "leader of Brazil" – reportedly after he was upbraided by Trump administration officials keen to avoid a full-blown diplomatic split with Brazil's actual leaders.

The amended letter also updated the out-of-date Brazilian coat of arms that had been used erroneously in the letterhead of the first version referring to the "United States of Brazil" – a name the South American country has not used since 1967.

Bolsonaro's flight – and his brief but bogus claim to be "president-elect" of one of the world's largest democracies – prompted an outpouring of opprobrium and ridicule.

"[This letter] seems to have been written by a foolhardy, loony halfwit," Flávia Oliveira, a prominent political commentator, told the network GloboNews.

The Estado de São Paulo's leader writers said: "Flávio's letter isn't worth the ink of this newspaper, but there's no way the embarrassment can be ignored," before savaging a man they called "a con artist of the highest order".

The Rio broadsheet O Globo said Bolsonaro's "shameful and sneaky" decision to abscond laid bare the "pathetic" nature of his political movement, Bolsonarismo, while the Folha de São Paulo said it exposed the true nature of the "authoritarian, ignorant, incompetent" Bolsonaro family.

Even Silas Malafaia, a pugnacious televangelist who is close to Bolsonaro's jailed father, Jair Bolsonaro, had harsh words. "Bolsonaro's kids are jackasses … A bunch of amateur morons," Malafaia was quoted as saying by O Globo.

Some observers see Bolsonaro's post-defeat getaway as proof that his dispirited movement is dead. "I think Bolsonarismo was defeated once and for all," Lula's chief foreign policy adviser, Celso Amorim, said this week, calling the result "the last gasp of a radical, irrational, lying right wing".

The Estado de São Paulo's editorial board agreed. "Flávio belongs to the past and will soon vanish into the basement of political irrelevance from which he should never have emerged," they predicted, urging conservatives to ditch Bolsonaro and throw their weight behind his ally Tarcísio de Freitas, the São Paulo governor.

Others warned Bolsonarismo would remain a powerful political force, even if the Bolsonaro family's leadership of the far-right movement was now in doubt.

Social media users were also merciless in their reaction to Bolsonaro's short-lived claim to be "president-elect". One meme invited supporters to attend his January inauguration – at Cinderella Castle in Walt Disney World, Orlando. Another parodied his movement's fascist-inspired slogan "God, homeland and family", which became "Goodbye, homeland and family".

Donald Trump has declined to publicly recognise the result of an election he has called "a very great embarrassment to the people of Brazil". But a US diplomatic cable obtained by the Folha de São Paulo called Lula's victory "surprising but definitive".

Asked if he saw Bolsonaro as Brazil's "rightful" leader, the US president replied: "I won't get involved."