KUALA LUMPUR, Malaysia—Malaysia’s ruling party said on Saturday that it expelled two of its best-known members and began investigating a third for backing the opposition in Wednesday’s Wednesday’snational election, a fresh sign that Prime Minister Najib Razak might be facing a tougher-than-expected battle to stay in power.
The two politicians expelled from the United Malays National Organization or UMNO, Daim Zainuddin and Rafidah Aziz, as well as Rais Yatim, who is under investigation, are closely associated with Mahathir...