Graft in army spending turns into a headache for Ukraine.

The removal of Ukraine’s minister of defense after a flurry of reports of graft and financial mismanagement in his department underscores a pivotal challenge for President Volodymyr Zelensky’s wartime leadership: stamping out the corruption that had been widespread in Ukraine for years.

Official corruption was a topic that had been mostly taboo throughout the first year of the war, as Ukrainians rallied around their government in a fight for national survival. But Mr. Zelensky’s announcement Sunday night that he was replacing the defense minister, Oleksii Reznikov, elevated the issue to the highest level of Ukrainian politics.

It comes at a pivotal moment in the war, as Ukraine prosecutes a counteroffensive in the country’s south and east that relies heavily on Western allies for military assistance. These allies have, since the beginning of the war, pressured Mr. Zelensky’s government to ensure that Ukrainian officials were not siphoning off some of the billions of dollars in aid that was flowing into Kyiv.

Just last week, the United States’ national security adviser, Jake Sullivan, met with three high-ranking Ukrainian officials to discuss efforts to stamp out wartime corruption. It comes as some lawmakers in the United States have used graft as an argument for limiting military aid to Ukraine.

Mr. Zelensky has responded to the pressure from allies and criticism at home with a flurry of anticorruption initiatives, not all of them welcomed by experts on government transparency.