With a Ukrainian military honor guard standing ramrod straight beside his coffin, Andriy Melnyk, a leader of a Ukrainian nationalist movement who died six decades ago — and who has been no less divisive after death than in life — lay in state in Kyiv before his reburial on Sunday. President Volodymyr Zelensky provided full state honors for the ritual, signaling a deep shift in Ukrainian politics after Russia’s invasion in 2022. Before then, Mr. Zelensky had kept nationalist politics at arm’s length; in the reburial, he embraced them. The remains of the long-dead World War II-era Ukrainian leader were exhumed in Luxembourg, where he had been buried after dying in exile in 1964, and returned to Ukraine. There was none of the raw grief of today’s war funerals. Melnyk led one of two factions of the Organization of Ukrainian Nationalists, including through a period of alignment with the Nazi army during its occupation of Ukraine, which was one of the bloodiest chapters of World War II. The Soviet Union signed a nonaggression pact with …