For weeks, newly appointed justice chief Cho Kuk has been dogged by allegations of corruption against his family, including his wife, who has been indicted on suspicion of faking academic credentials to help her daughter gain admission to medical school – an explosive charge in a society where academic achievement is seen as the ultimate pathway to success. Prosecutors also accuse Cho’s wife of financial irregularities and his brother of committing bribery and embezzlement through a family-run school foundation.

Moon appointed Cho, a law professor and liberal icon, as the top law official last month in the face of fierce political opposition, arguing that the allegations against his family were not proven and he was best placed to carry out much-needed reform of the prosecutions system, which has long been plagued by accusations of political bias and abuse of power. Unlike in many countries where powers are shared more evenly with the police, South Korean prosecutors have exclusive authority to indict suspects and request warrants, and are empowered to supervise and direct police investigations.

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Cho, who previously served as senior presidential secretary for civil affairs and is widely considered a future presidential contender, has denied any wrongdoing and vowed not to interfere with the investigation into his family. The presidential office, also known as the Blue House, did not respond to a request for comment.

In the last two weeks, student groups and conservative activists have staged large protests in Seoul calling for the resignation of both Cho and Moon, including a rally on Wednesday for which local media and organisers offered diverging crowd estimates ranging from hundreds of thousands to 5 million people.

In an opinion poll published by Hankook Research on Thursday, 54 per cent of respondents said Cho should not have been appointed to his position.

To many South Koreans, the scandal has served as another example of the unearned advantages enjoyed by those born with a “golden spoon”, said An Junseong, an adjunct professor at Yonsei University in Seoul, referring to a common expression used to describe the country’s wealthiest.

“Most Koreans view the Cho Kuk controversy as a revelation of a new type of unfair competition in the education field,” An said.

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“His daughter’s prestigious education path, from a foreign-language high school to a medical school, has been meticulously designed and orchestrated in concert with several professors who appear to have either some ties with his family education business or political interest in establishing and maintaining a good relationship with the senior presidential secretary for civil affairs, one of the most powerful persons at the Blue House.”

Amid mounting public anger, Moon’s approval rating this week hit a record low of 44.4 per cent, according to local pollster Realmeter, having soared into the mid-80s during the early months of his presidency.

Hong Deuk-pyo, a professor emeritus of political science at Inha University, said the scandal exposed the apparent hypocrisy of a close confidante of the president who held himself up as righteous and incorruptible.

“The situation has tarnished the image President Moon has tried to craft of being a trustworthy president,” Hong said.

Supporters of Cho, who have staged rallies backing the embattled minister, have accused prosecutors of targeting his family because of his push to curb their powers such as by reducing their authority to direct investigations and limiting interrogations to a maximum of eight hours at a time.

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“Cho promised radical reforms of the prosecutors’ office if he became minister of justice,” said Shin Kwang-yeong, a sociology professor at Chung-Ang University. “The prosecution has been the most invincible organisation which has been an instrument of authoritarian rule in the past, abusing the power of its monopoly on indictments.”

Shin said the controversy in reality reflected a heated conflict between “pro-reformers and anti-reformers”, accusing conservative media of publishing unverified leaks from prosecutors.

“Magnified allegations have affected public opinion,” he said.

Allegations of corruption are common in South Korea’s scandal-plagued politics, with three out of seven presidents given prison time for various crimes since the beginning of the democratic era in 1987. 

Roh Moo-hyun, South Korea’s last liberal president and Moon’s political mentor, took his own life in 2009 as prosecutors were investigating his family on suspicion of corruption.

Moon’s conservative predecessor, Park Geun-hye, the daughter of a former dictator, was impeached over a massive corruption and influence-peddling scandal revolving around a mysterious aide, Choi Soon-sil, who solicited favours that included gaining her daughter’s admission to a prestigious university in Seoul. Park was sentenced to more than 30 years in prison in separate trials last year for offences including abuse of power, bribery and interfering in the 2016 parliamentary elections. Park’s predecessor, former Hyundai executive Lee Myung-bak, was sentenced to 15 years in jail last year for bribery and embezzlement.

In his inaugural speech, Moon pledged to be a “clean” president who would bring an end to South Korea’s “unfortunate history” of presidential scandal. Nearly halfway into his five-year term, that promise is facing its biggest test yet.

“People have accumulated anger against the current Moon regime in South Korea since the impeachment of Park Geun-hye,” said Dong Yon Kim, a former journalist and air force officer who now works at KORGAD, a national security-focused NGO, adding that the latest controversy fuelled existing disillusionment with the economy and Moon’s policy of rapprochement with nuclear-armed North Korea.

“It is a mixed form of anger which is driven by multiple unfair, senseless processes of government.”