DAP supremo Lim Kit Siang said Pakatan Harapan needs to find a formula to win over the people's support following its defeat in the Semenyih by-election.
However, Lim said one way forward that Harapan must avoid is trying to outdo Malay nationalist party Umno and Islamist party PAS.
"The challenge for Harapan after the Semenyih by-election defeat is to find a formula to be able to continue to inspire hope and support among Malaysians that Harapan is committed to the building of a New Malaysia for the benefit of all Malaysians and future generations and not to out-Umno Umno or out-PAS PAS.
"The year 2019 will be a most decisive year in the nation’s history which will decide whether the New Malaysia the Harapan coalition of Bersatu, PKR, Amanah and DAP wants to build is a work-in-progress or a sheer chimera," he said in a statement today.
Lim said Harapan needs to convince Malaysians it is committed to the New Malaysia objective and that it was making progress.
He stressed that nation-building should not be a zero-sum game, but a win-win formula.
"We must fight for the rights of the Malays, but not at the expense of the non-Malays.
"We must fight for the rights of the Chinese in Malaysia, but not to the detriment of the non-Chinese.
"We must fight for the rights of the Indians in Malaysia without being a threat to the non-Indians in Malaysia. Similarly for the Kadazans, Ibans and Orang Asli communities in Malaysia," he said.
Last Saturday, BN wrested the Semenyih state seat from Harapan, capturing the constituency with a 1,914-vote majority.
Harapan won the seat in the 2018 general election by a landslide due to votes being split between PAS and Umno.
However, both parties co-operated closely for this by-election, which was called following the passing of its Harapan incumbent Bakhtiar Mohd Nor.