Hardcore supporters of Brazil’s president, Jair Bolsonaro, have urged his followers to flood the streets in defence of their leader on Sunday amid mounting conservative angst over the far-right populist’s anarchic opening act in office.

Bolsonaro swept to power last October, his insurgent campaign turbocharged by widespread revolt at the corruption and economic misrule of the Brazilian left.

But seven months later, with Brazil’s economy stuck in the doldrums, political infighting raging, and Bolsonaro facing protests at home, rejection overseas and questions over corruption in both his party and his family, his approval ratings have plummeted to historic lows and several prominent supporters are publicly voicing regret.

“I had to choose someone, and that someone was Bolsonaro. But he has shown he doesn’t have the slightest intellectual or emotional capacity to administer Brazil,” the rightwing singer Lobão complained last week in an interview with Valor Econômico, Brazil’s answer to the Financial Times. “It’s obvious the government is going to collapse,” he added.

Brazil's Bolsonaro dismisses 'imbecile' students as he faces biggest protests yet Read more

Reinaldo Azevedo, a rightwing commentator, offered an equally dismal evaluation. “If … Bolsonaro continues to listen only to the horde of lunatics that surrounds him, he won’t finish his term,” he warned in an article about Brazil’s “shallow and petty” leader.

In an editorial headlined The Bolsonaro Threat, the conservative newspaper O Estado de São Paulo – which has emerged as a particularly ferocious critic of Brazil’s president – said he had “shown a shocking unpreparedness for the job”.

That might be remedied by competent ministers, it argued. But Bolsonaro had packed his administration with “toadies whose only function seems to be confirming the president’s daydreams”.

Bolsonaro has reacted to the intensifying barrage of friendly fire by escalating his populist rhetoric and calling diehard supporters to the streets. “The big problem is our political class,” Bolsonaro, a career politician who falsely paints himself as a political outsider, claimed this week. “We have a unique opportunity to change Brazil. But I won’t be able to do it alone.”

Fernando Sampaio, an activist for Bolsonaro’s Social Liberal party (PSL) in the south-eastern state of Minas Gerais, said he would heed that call on Sunday. “I feel it is my duty and obligation to take part,” he said. “The Bolsonaro government has come to cause a rupture in the current system – and that is what he has been doing … But he cannot do this alone … [He] needs to mobilise the people.”

But critics – including many on the right – have condemned Sunday’s demonstrations as a dangerous attempt to radicalise Brazil’s politics and intimidate its institutions.

Several fliers promoting the marches depict them as part of a Bolsonarian bid to close Brazil’s congress and supreme court. One online advert features the image of a Knights Templar warrior carrying Brazil’s green and yellow flag and the slogan “Let’s save Brazil”. Another urges Bolsonaro supporters to “invade” the capital, Brasília, to give Brazil’s political elite a taste of “the rage of the people”.

Janaína Paschoal, a PSL congresswoman who was instrumental in Bolsonaro’s rise and nearly became his presidential running-mate, urged fellow conservatives to shun his attempt to sow “chaos”. “I didn’t stay silent over the crimes of the left and I will not remain silent about the irresponsibility of the right,” she tweeted.

Kim Kataguiri, another prominent rightwinger, said his group, the Free Brazil Movement (MBL), would not attend the protest or engage in “blind idolatry”.

Monica de Bolle, director of Latin American studies at Johns Hopkins University, said such opposition highlighted growing dissatisfaction among Bolsonaro voters at his administration. “They just see dysfunction … If we think Trump is unprepared for office, Bolsonaro is 100 times that … This is the reality that’s sinking in.”

Steven Levitsky, a Harvard University professor of government, said he was not surprised that, having failed to build coalitions within Brazil’s highly fragmented Congress to pass key reforms, Bolsonaro would try to attack it with “demagogic appeals to the masses” such as Sunday’s protests.

“Autocrats – and I think it is pretty safe to call Bolsonaro a pretty autocratic leader – like to govern unilaterally, and Brazil is difficult to govern unilaterally,” he said.

But with Bolsonaro’s approval ratings this week sinking to under 29%, Levitsky said he doubted such tactics would work. “This seems a very risky endeavour for Bolsonaro, more likely to end in his isolation,” he said.

“Bolsonaro has made a number of errors and his public support has flagged as a result – and that is probably a good thing for democracy. It’s always better to have an inept and unpopular autocrat in power, than a talented and popular one. I prefer Trump to Orbán any day.”