The overnight rally by electoral reform group Bersih beginning this afternoon is bringing together strange bedfellows from opposite sides of the political divide, a reflection of the political flux that Malaysia finds itself in.
There is no doubt opposition parties like the Democratic Action Party (DAP) and jailed de facto opposition leader Anwar Ibrahim's Parti Keadilan Rakyat (PKR) will support the march as they had done in three previous Bersih street protests.
But the absence of Parti Islam SeMalaysia (PAS), which provided the bulk of participants and logistical support in the earlier marches, is likely to dampen the turnout of demonstrators who will call for the resignation of embattled Prime Minister Najib Razak.
What's unusual is that the protesters may be joined by supporters of the ruling Umno, of which Datuk Seri Najib is the president.
Mr Najib has denied any wrongdoing over US$700 million (S$980 million) in "political donations" deposited into his personal accounts, and has been fighting off threats to his leadership since reports of the money surfaced on July 3.
He ejected from his Cabinet members of his Umno party, including deputy president Muhyiddin Yassin and vice-president Shafie Apdal, after they criticised him over the funds.
These Umno stalwarts' open criticism appears to have paved the way for other Najib allies to adopt a laissez-faire attitude towards Bersih. Thus, Sarawak chief minister Adenan Satem has acknowledged "civil society's right to assembly".
Malay rights organisation Perkasa, a pro-establishment group, has also said it will not stop its members from attending the Bersih rally, whereas in the past it organised counter-rallies against Bersih protests. "We are not stopping them (our members), but we are not supporting it either. We respect the people's right to march but we are also concerned about national safety," said its president Ibrahim Ali.
While it is unlikely that Umno members will join the rally in full force, those opposed to Mr Najib may use a significant turnout as leverage against him, say analysts.
"There is no way Najib will resign just because of Bersih. But the biggest impact is on sentiment. As at previous Bersihs, Umno will label participants as troublemakers. But this time, those against Najib will use it to say that Umno will lose support because of his leadership," think-tank Ideas chief Wan Saiful Wan Jan told The Straits Times.
Already, Langkawi Umno division member Anina Saaduddin has filed a suit against Mr Najib over the funds in his accounts. She faces expulsion according to party rules.
Bersih's choice of date and venue has been controversial, as it coincides with an Independence Day countdown held every year at Merdeka Square. If it succeeds in keeping its supporters on the ground up to 9pm tomorrow - over 30 hours from the 2pm kick-off today - it will also overlap with Mr Najib's televised national address.
The PAS - whose feud with the DAP over Islamic criminal laws led to the break-up of an opposition alliance that includes the PKR - said it was not consulted on the selection of the date and would not mobilise for the rally due to a clash of plans.
A poll by independent researcher Merdeka Centre found that 43 per cent of those surveyed were for the march and 47 per cent against.
Those against the march largely cited fear of violence and chaos. At all three previous Bersih rallies, the police dispersed the marchers with tear gas and water cannon, and these tools will be part of the arsenal of the 4,000 policemen deployed this time.
Bersih supporters will march towards Merdeka Square from five nearby rallying points but, with police expected to cordon off the square and thereby keep the groups apart, a likely flashpoint will be the agitation of protesters who want to converge with the others.