AFTER FIVE months in office, Ukrainian President Volodymyr Zelensky faces a confluence of challenges in the coming weeks. Any competent U.S. administration would be waging vigorous diplomacy as decisions critical to the future of the West are made. The Trump administration is absent, or worse.

Mr. Zelensky is seeking to meet with Russia’s Vladi­mir Putin and the leaders of France and Germany in an attempt to revive a moribund plan for ending the war in eastern Ukraine. Separately, his administration faces a year-end deadline for negotiating a new deal on transit shipments of Russian gas to western Europe through Ukraine — a key source of revenue for Kyiv that has led to sharp bilateral conflicts in the past.

Last but not least, Mr. Zelensky is seeking a new agreement with the International Monetary Fund, which has provided essential loans to Ukraine and whose imprimatur is needed to reassure other Western lenders and investors. That, in turn, will require the 41-year-old president, a political neophyte, to demonstrate his independence from the oligarch who backed his campaign and, previously, his television career. The tycoon, Ihor Kolomoisky, has spooked the IMF by seeking to reverse the nationalization of a bank he has been accused of looting or to receive billions in compensation.

In short, Ukraine’s leadership badly needs help from the United States, which has been its closest ally in resisting Russia’s aggression and pursuing needed reforms. Unfortunately, senior U.S. officials are nowhere to be seen in Kyiv — thanks to the destruction of U.S. diplomacy there by President Trump and his personal lawyer, Rudolph W. Giuliani.

Mr. Giuliani persuaded Mr. Trump to withdraw the competent U.S. ambassador to Ukraine, Marie Yovanovitch, who was challenging Mr. Giuliani’s shady associates. The post is vacant; the charge d’affairs in Kyiv, William B. Taylor, is due to testify to Congress Tuesday about the attempt by Mr. Trump and Mr. Giuliani to induce Mr. Zelensky to launch investigations of Democrats in exchange for a White House meeting and military aid.

The State Department’s deputy assistant secretary covering Ukraine, George Kent, told Congress that he had been stripped of responsibility for the country earlier this year. And Kurt Volker, the veteran diplomat who since 2017 had represented the United States in the Ukraine-Russia peace talks, stepped down from his position last month following disclosure of his involvement in the pressure campaign.

That leaves Mr. Zelensky to the mercies of Mr. Putin, who seeks the de facto dismemberment of Ukraine as the price for a peace settlement, and French President Emmanuel Macron, who has made clear he would like to lift the European Union sanctions against Russia. Meanwhile, Mr. Zelensky will lose credibility in financial capitals unless he breaks with Mr. Kolomoisky. But there is no one in Washington to make that case to him: On the contrary, Mr. Trump has been pressing for his own political favors, while Mr. Giuliani is allied with some of Ukraine’s least savory officials and businessmen.

Having struggled for years to establish its independence from Russia, combat corruption and jump-start its economy, Ukraine had a fragile opportunity for a breakthrough with the election of Mr. Zelensky, who ran on a platform of draining the swamp in Kyiv. He may yet succeed. But if he does, it will be despite the toxic influence of the United States.

Read more: