APRIL 21

Volodymyr Zelensky is elected president of Ukraine. Soon after, allies of President Trump’s personal lawyer Rudolph W. Giuliani relay a message that Mr. Giuliani wants to meet with him. Mr. Zelensky puts him off, noting that he has not yet taken office.

May 6

The State Department announces that Marie L. Yovanovitch, the American ambassador to Ukraine, has been recalled to Washington months ahead of schedule after Mr. Giuliani and his allies spread unfounded allegations that she was disloyal to Mr. Trump. About the same time, John R. Bolton, the White House national security adviser, warns a deputy: “Giuliani’s a hand grenade who’s going to blow everybody up.”

MAY 10

Mr. Giuliani tells Fox News that Mr. Zelensky seems surrounded by operatives allied with the Democratic Party and “enemies of the president, and, in some cases, enemies of the United States.” A few days later, an associate of Mr. Giuliani’s warns the Ukrainians that American aid could be withheld, according to the associate’s lawyer, although others dispute that timing.

MAY 23

In an Oval Office meeting with Mr. Trump, Kurt D. Volker, then the special envoy to Ukraine; Gordon D. Sondland, the United States ambassador to the European Union; and Rick Perry, the energy secretary, all describe Mr. Zelensky as a committed reformer who deserves American support. All three attended Mr. Zelensky’s swearing-in in Kiev three days earlier.

Mr. Trump replies that Ukraine is full of “terrible” and corrupt people who had “tried to take me down.” He orders the officials to coordinate future Ukraine matters with Mr. Giuliani.