Former Umno strongman Dr Mahathir Mohamad is now firmly behind the opposition in their fight against Prime Minister Najib Abdul Razak.

However, The Economist in an article questioned whether the Parti Pribumi Bersatu Malaysia (Bersatu) chairperson would be fully committed to toppling Umno.

"One big worry for the opposition is how far Dr Mahathir’s conversion goes. No one doubts his visceral disdain for Prime Minister Najib Razak.

"Less certain is whether, given a choice, he and his party would stop short of ousting Umno altogether," the international business and finance magazine said in a comment piece today.

The piece, titled "Mahathir Mohamad. Can a leopard change its spots?" noted that Umno splinter groups had in the past ended up re-joining the party.

However, it cited Mahathir as saying that there's "no way Bersatu would consider a deal that leaves Umno in government, even under a new leader".

Bersatu was formed by Mahathir and other Umno rebels, such as former party deputy president Muhyiddin Yassin, as a vehicle to oppose Najib and BN in the next general election.

The new party is currently working with Pakatan Harapan parties PKR, DAP and Amanah, although it plans to work things out with PAS as well, to ensure straight fights with BN.

The Economist also noted that while Mahathir has many fans, especially among the youth who don't remember his 22-year reign as prime minister, winning more than a handful of seats would be difficult for Bersatu.

It said liberal factions would be "much happier if Dr Mahathir were more contrite about his part in the country’s present predicament".

The comment piece says: "He is probably right to insist that, on his watch, corruption was more limited than the lurid misdeeds of which the present leadership stands accused.

"But it was under his tenure that Umno’s leaders became so hard to dislodge, and Malaysia’s courts so cowed."