In its editorial on Sept 2, 2015, The Nation says that recent protests in Malaysia over a graft scandal threaten decades of effort to build the country.

The man who kick-started Malaysia's ambitious agenda to become fully developed by 2020 is now at loggerheads with the man overseeing the home stretch of that long-term scheme.

Amid mass protests on a scale not seen in Kuala Lumpur in years, Mahathir Mohamad, the former but still-influential prime minister, has called for the resignation of Najib Razak from the highest political office over a massive corruption scandal.

All of a sudden Malaysia, which has enjoyed relatively stable politics of late, is looking like it might have caught Thailand's chronic disease.

Similarities and differences are readily ascertained.

Among the shared traits, some of Premier Najib's friends have turned into enemies, the allegations against him are largely of a financial nature, and it's doubtful they will sway his grassroots support base, in this case the country's dominant Malay population.

Strikingly, participants in the mass protests - now taking a temporary hiatus - are wearing yellow garb, and most are better off financially than his supporters.

If all that sounds familiar, at least no one has thus far mentioned the possibility of a military coup.

The demonstrations pose the biggest single challenge yet to Najib's six-year rule.

His political fortunes have long been associated with the perennial dominance of the United Malays National Organisation (Umno), the political umbrella group that has controlled Malaysia since bringing about independence from Britain in the 1950s.

Its pro-independence slogan was "Bad local rulers are better than good foreign rulers", a sentiment given ample exercise over the decades.

The woeful irony in Umno's ties to Najib is that it is also connected to Mahathir.

The current corruption scandal involves mysterious payments of almost US$700 million (S$990.3 million) into bank accounts linked to Najib.

The country's anti-corruption commission has said the money came from unspecified Middle Eastern donors, but the belief is widespread that the cash hoard is related to huge debts run up by a state investment fund.

The prime minister has insisted he did nothing wrong, but he has failed to convince sceptics with his explanations about the money's source.

Malaysia is no stranger to social tensions. In 1969 racial conflict escalated into riots, with Umno blamed in part for an economic policy privileging Malays.

Attempts to mend the rift were made, with measures aimed at pacifying the minorities economically.

At an anti-government uprising in 2012, security forces used tear gas and water cannon against protesters. Iron-handed treatment of political dissenters is not unusual in Malaysian politics, continuing under Mahathir as well.

That unrest was followed by elections in which the opposition claimed the lion's share of the popular vote, and yet an Umno-led coalition retained its parliamentary majority.

It's too soon to conclude that national harmony is now in danger again, but the current situation, if not resolved quickly, could become a powder keg.

Najib can thank an annual national holiday period for quelling the uprising for now, but his worries are not going to evaporate. Further protests are being planned outside Kuala Lumpur, leaving Southeast Asia's third-largest economy facing the possibility of drawn-out political uncertainty.

As matters stand, the country's ambition to be fully developed within five years seems less likely to succeed. Najib - leading Malaysia into the home stretch toward that goal - is in dire trouble, and the road ahead will only get bumpier, no matter what transpires.

If the prime minister is not corrupt, the scale of the protests alone is worrisome. If he is, Malaysians have much more serious eventualities to fret about.

* The Nation is a member of The Straits Times media partner Asia News Network, a grouping of 22 newspapers.