THE TIGHTENING NOOSE:

Mr. Poroshenko's campaign included trade deals that were politically expedient for Mr. Trump, meetings with Rudolph W. Giuliani, the freezing of potentially damaging criminal cases and attempts to use the former Trump campaign chairman Paul Manafort as a back channel.

From the start, Mr. Poroshenko's aides also scrambled to find ways to flatter the new American president -- advising their boss to gush during his first telephone call with Mr. Trump about Tom Brady, the star New England Patriots quarterback whom Mr. Trump has long admired.

An examination of the first year of Mr. Trump's dealings with Ukraine shows how the White House also saw the relationship as a transactional one that could help Mr. Trump politically.

Mr. Poroshenko, so eager to gain favor as Russian-backed separatists were escalating a fight against the Ukrainian military, did his part to encourage this belief. He helped plant the seeds for Mr. Trump's July quid pro quo request to his successor, Volodymyr Zelensky -- a request that prompted the impeachment inquiry into whether he manipulated American policy toward Ukraine for personal gain.

Mr. Poroshenko's strategy yielded results. The Trump administration reversed an Obama-era moratorium on sales of lethal weapons that Ukraine sought for its fight against the separatists in the country's east.

Near the end of 2017, just as the government in Kiev was trying to get final approval from the Trump administration on the sale of the Javelin anti-tank weapons, Mr. Poroshenko's prosecutor general, Yuriy Lutsenko, had begun freezing cases in Ukraine relevant to the Mueller investigation, including an inquiry tracing millions of dollars that Ukrainian political figures paid to Mr. Manafort.

Now, impeachment investigators are examining the two years of interactions between Mr. Trump and Mr. Poroshenko, according to a congressional Democrat. And Mr. Zelensky's team is researching back-channel communications between Ukrainian officials and Americans from both political parties going back to 2017, according to a Ukrainian with knowledge of the effort.

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