KUALA LUMPUR (Reuters) - Malaysian Prime Minister Najib Razak faces a test of his popularity this week in two by-elections that come hard on the heels of calls by the country's former long-time leader, Mahathir Mohamad, for him to step down.
The influential Mahathir, 89, has intensified attacks on Najib in recent weeks, criticising him for his management of the economy and scandals arising from debt-laden state fund 1MDB and the murder of a Mongolian model nine years ago.
Mahathir has said the ruling United Malays National Organisation risks losing the next election, due by 2018, if Najib remains its leader. A poor showing in this week's by-elections could weaken the premier's position.
Najib's government has drawn criticism over a new tax on goods and services, with 10,000 demonstrators turning out last Friday in the biggest show of public dissent since protests sparked by allegations of election fraud after Najib's re-election two years ago.
The ruling Barisan Nasional coalition, which has led the multiethnic southeast Asian nation since independence in 1957, is widely expected to win Tuesday's election for its traditional stronghold of Rompin in the eastern state of Pahang.
But anything short of a resounding victory would be seen as a reflection on Najib's leadership, political analysts said.
"The results would be used to test whether Najib is a poison pill or a magic wand for his party," said Oh Ei Sun, a senior fellow at the S. Rajaratnam School of International Studies.
"If the win margin diminishes compared to previous years, then one could argue that Najib's leadership is dented."
Risks to Najib stem largely from factions in his own party since opposition leader Anwar Ibrahim, arguably Malaysia's most charismatic politician, was convicted of sodomy and jailed in February, after a trial he decried as politically motivated.
On Thursday, Anwar's wife, Wan Azizah Wan Ismail, stands for her husband's seat in the northern island of Penang, but could struggle to win, as ties among the three-party opposition alliance, the Pakatan Rakyat, have frayed.
A push by one member, Parti Islam se-Malaysia (PAS), to introduce an Islamic penal code has alienated it from Anwar's party and the ethnic Chinese Democratic Action Party. PAS threatened to boycott the alliance's by-election campaign.
"This internal squabbling will affect the election result," said Wan Saiful Wan Jan, of the Institute for Democracy and Economic Affairs (IDEAS) think tank in Kuala Lumpur.
"This was supposed to be a safe seat for Pakatan. But now the expectation is that BN will get more votes in the seat than before."
Reporting by Praveen Menon; Editing by John Chalmers and Clarence Fernandez