And even amid the impeachment scandal in Washington, and with far less Western political assistance than his predecessor, Mr. Zelensky is making tentative progress toward ending the bloodshed in the country’s east, where Russia continues to wage a war that has cost over 13,000 lives. Mr. Zelensky met with his Russian counterpart, Vladimir Putin, in December. Despite worries that he would capitulate to Russia, he stood firm. In addition to a prisoner exchange that took place before the new year, the leaders agreed to new civilian crossings and a demining plan. What’s more, Mr. Zelensky laid out clear “red lines” he will not cross in future negotiations: Ukraine will not be federalized, allow Russia to influence its political decisions or acquiesce to Russian control of any of its territories, including Crimea.

American influence would be most useful for these peace negotiations and anticorruption efforts. A skilled replacement for Kurt Volker, America’s former special envoy to the country, will ensure that Ukraine isn’t left with an outcome that threatens its sovereignty. A more unified American voice might help in other areas, too: Worries remain about the oligarch Ihor Kolomoisky’s influence over the government, as well as the new political elite’s relative inexperience. High-level American pressure could provide the guidance the Zelensky administration needs to continue to govern well, free of oligarchic influence.

Resolving these issues is in America’s interests. A democratic, prosperous and peaceful Ukraine can serve as a model for other transitional democracies — pushing back on Russian influence and adventurism and making room for citizen participation in government. American diplomats and civil servants continue to diligently assist their Ukrainian counterparts to achieve these goals, but their message is undercut by the drumbeat of conspiracy and accusations of corruption reverberating in the halls of Congress.

Members of Congress who were once among the most vocal supporters of Ukraine, including Senator Lindsey Graham, who has visited Ukrainian troops on the front lines in the country’s east, are now undercutting the progress Kyiv has made in the last six years. They claim that Ukraine is irredeemably corrupt despite the successful reforms they advocated under the previous president, Petro Poroshenko. These misplaced corruption concerns fuel unfounded narratives about Hunter Biden, Ukrainian election interference, the CrowdStrike conspiracy theory and secret cabals of “bad guys” within Ukrainian society allegedly working against Mr. Trump.

It is a dizzying array of falsehoods meant to confuse Congress and the American people, and everyone involved knows it. In recently released text messages, Rudy Giuliani, the president’s personal attorney and kingpin of Ukraine conspiracy theories, even admitted his fantasy about Ukrainian election interference is baseless.