In a matter of months, President Trump and his personal lawyer, Rudolph W. Giuliani, have twisted U.S. policy in Ukraine to their personal ends, touching off turmoil inside the White House and State Department and weakening — perhaps critically — a bilateral relationship that is crucial to containing Russian aggression in Europe.

The story of Trump’s strongarming of Ukrainian President Volodymyr Zelensky is first and foremost one of Trump’s abuse of his presidential power in pursuit of personal political gain. But it is also an epic example of how Trump has destroyed U.S. diplomacy in places around the world where, for years, it had worked smoothly and relatively effectively despite the growing partisan polarization in Washington.

As one of the relatively few U.S. journalists who has followed Ukraine closely over the years, I find that the saddest part of this story has been watching a once-cohesive community of U.S. diplomatic pros on Ukraine be crushed as it tried to contain and manage the hurricane-like intervention of Giuliani and Trump. The whistleblower’s complaint offers a partial picture of this unraveling, and I have heard more in several conversations with longtime sources.

Though Trump never had a positive view of Ukraine, the trouble really started with Giuliani, who has a record of working for and with the very Ukrainian actors that U.S. policy has aimed to marginalize: shady business executives and corrupt politicians with ties to Russia, organized crime or both.