By Asia analyst Alice Donald

When Malaysian Prime Minister Mahathir Mohamad sacked his deputy and rival, Anwar Ibrahim, earlier this month, on charges ranging from sodomy to treason, he clearly did not expect significant defiance.

When Mr Anwar then began a nationwide political roadshow, timed to cause maximum embarrassment during the Commonwealth Games, the authorities held back, no doubt hoping the crowds would soon disperse.

Neither calculation was correct. Instead, the political assassination of Mr Anwar has stunned the country and produced a remarkable new phenomenon in Malaysian politics.

Not since 1974, when Mr Anwar himself led a radical Islamic student movement, has Malaysia seen such spontaneous street protests.

Now middle class wants reform

The crucial difference this time is that the crowds include Malaysians of all races and classes including, most significantly, the new middle classes, who are articulating demands for reform previously unthinkable in the rigidly-controlled political culture of Malaysia.

It is not yet clear whether the momentum can be maintained now that the galvanising figure of Mr Anwar has been removed.

Mr Anwar's wife, Wan Azizah Wan Ismail, has stepped into his shoes, and will attract much sympathy. But the spontaneous and broad-based nature of the protests means that they necessarily lack defined common goals.

The middle classes who have flocked to Mr Anwar's cause may ultimately hold back out of fear of social dislocation. Nor is it yet clear whether Mr Anwar's traditionally Muslim power base can really assimilate other racial and religious groups, such as the ethnic Chinese.

Anwar sides with opposition parties

One possibility is that Anwar supporters will join forces with Malaysia's established opposition parties. Indeed, Mr Anwar himself appeared to signal that this was likely by joining rallies with the leaders of the multi-racial Democratic Action Party and the Islamist opposition party, PAS.

However, the political space in which they can operate is becoming ever smaller. Dr Mahathir has an absolute grip on the ruling UMNO party and the government apparatus.

His decision to sever Malaysia's links with the global financial system by imposing capital controls shows just how decisively he is prepared to act against what he sees as external threats.

By eliminating those voices which questioned his unorthodox economic policies, and shattering the long-planned succession to Mr Anwar, he has raised the stakes even further.

Mahathir walks a tightrope

But this very concentration of power leaves Dr Mahathir exposed as never before. Any more policy reversals or capricious gestures, and already wary investors may finally desert Malaysia.

Nor can Dr Mahathir endlessly rely on the loyalty of other senior party figures, particularly those who may now aspire to succeed him.

Above all, Dr Mahathir's aura of invincibility has been severely dented. The jeering of the crowds is an attack not just on his personal authority but on the values he cherishes. As each side considers its next move, they must be acutely aware that Malaysia is now sailing in uncharted waters.