Secretary of State Marco Rubio met with Russian Foreign Minister Sergey Lavrov in Malaysia Thursday at a meeting of the Association of Southeast Asian Nations. The meeting put the Russia-Ukraine war at the center of a trip that was meant to strengthen alliances in Southeast Asia.

Mr. Rubio’s efforts have been overshadowed by new tariff threats that President Trump made to 14 foreign leaders, which have infuriated the target governments, including Malaysia, the host of the mee...