Prime Minister Najib Abdul Razak will apparently take down all his opponents, except one - his arch nemesis Dr Mahathir Mohamad.

Despite his penchant for suing his critics, the latest being former MCA president Dr Ling Liong Sik, Najib has not threatened legal action against Mahathir who has even gone to the extent of accusing the prime minister of theft.

So why the kid gloves for Mahathir?

Political analyst Wan Saiful Wan Jan ( photo ) said while Najib's selective persecution is baffling, it is likely that the prime minister realises Mahathir can't force him to resign

"In the beginning, he (Najib) was concerned about what will happen to his own position if he were to handle Mahathir in the wrong way.

"But now Najib realises his position is quite solid and safe regardless of what Mahathir says. The reality is he doesn't have to go anywhere unless he wants to," he told Malaysiakini.

"(Plus) suing Mahathir is quite suicidal," he said, noting that Mahathir still has influence and support in Umno.

Asked to elaborate how Najib could feel secure despite Mahathir's incessant assault, Wan Saiful said it was because the prime minister was the most powerful man in the country.

"The reality is power is not just concentrated in Putrajaya, but in Najib himself as a person.

"With that level of concentration, Najib becomes the most powerful person in the country and there's absolutely nothing that can be done to remove him," he said.

He said while Mahathir can sow a negative perception towards Najib in the people's mind by repeating allegations, who controls Seri Perdana is out of his hands.

"It's up to Najib whether or not he wants to go, and ironically this is the legacy of Mahathir," he added.