“It wasn’t easy for me to join a movement that was not happy with me in the past, but the effort to topple Najib is greater than my feelings,” Mahathir said in a speech after his nomination. “Therefore, I am willing to cooperate and listen to the criticism toward my old party.”

A victory could also potentially pave the way for former Mahathir foe Anwar to become the prime minister.

Mahathir and Anwar’s wife Wan Azizah Wan Ismail will be the Pakatan Harapan coalition’s candidates for the premier and deputy prime ministerial posts respectively, secretary general Saifuddin Abdullah said at the alliance’s convention.

If the opposition wins, the component parties have agreed to immediately commence the legal processes to obtain a royal pardon for Anwar, Saifuddin said.

“So that Anwar could immediately play a role in the federal government and subsequently be proposed as a candidate for the eighth prime minister,” he said.

A December survey by Merdeka Centre for Opinion Research showed that Najib’s coalition may regain its two-thirds majority in parliament, the Malaysian Insight reported.

“Mahathir will be a tough opponent to Najib,” said Ibrahim Suffian, programme director at Merdeka Centre. “So while the survey presently indicates the situation as being uphill for Pakatan, we still have perhaps two to three months to the election, which is at least half a lifetime in politics.”

The Mahathir-Anwar coalition and their endorsement of each other is a turnaround from their bitter feud that has shaped Malaysia’s political landscape for nearly two decades.

Anwar was once a protégé of Mahathir, and the rising star of Malaysian politics, but they had a falling-out in the late 1990s. Soon afterwards, Anwar was jailed on charges of sodomy and graft, after being sacked as the deputy prime minister. He denied the charges, dismissing them as politically motivated.

Anwar later led an opposition alliance to stunning electoral gains in 2013. Najib’s Barisan Nasional coalition lost the popular vote in that election, but managed to stay in power after winning a majority of the seats in parliament.

But Anwar was convicted and jailed again in 2013 for sodomising a former aide, a charge he and his supporters describe as an attempt to end his career.

The sodomy conviction disqualifies Anwar from political office and from contesting the next election. A royal pardon, however, would let him contest.

Opposition to Prime Minister Najib has brought Anwar and Mahathir back together, with their parties now working in the opposition coalition.

Najib has been embroiled in a corruption scandal involving state fund 1Malaysia Development Berhad (1MDB). In civil lawsuits, the US Justice Department has alleged that about US$4.5 billion was misappropriated from 1MDB.

The fund has denied any wrongdoing and Najib, who founded 1MDB, has denied all allegations of corruption against him and was cleared of wrongdoing by Malaysia’s attorney general.

Additional reporting by Bloomberg