[Read our 5 takeaways from John Bolton’s book.]

WASHINGTON — More than two months before he asked Ukraine’s president to investigate his political opponents, President Trump directed John R. Bolton, then his national security adviser, to help with his pressure campaign to extract damaging information on Democrats from Ukrainian officials, according to an unpublished manuscript by Mr. Bolton.

Mr. Trump gave the instruction, Mr. Bolton wrote, during an Oval Office conversation in early May that included the acting White House chief of staff, Mick Mulvaney, the president’s personal lawyer Rudolph W. Giuliani and the White House counsel, Pat A. Cipollone, who is now leading the president’s impeachment defense.

Mr. Trump told Mr. Bolton to call Volodymyr Zelensky, who had recently won election as president of Ukraine, to ensure Mr. Zelensky would meet with Mr. Giuliani, who was planning a trip to Ukraine to discuss the investigations that the president sought, in Mr. Bolton’s account. Mr. Bolton never made the call, he wrote.

The previously undisclosed directive that Mr. Bolton describes would be the earliest known instance of Mr. Trump seeking to harness the power of the United States government to advance his pressure campaign against Ukraine, as he later did on the July call with Mr. Zelensky that triggered a whistle-blower complaint and impeachment proceedings. House Democrats have accused him of abusing his authority and are arguing their case before senators in the impeachment trial of Mr. Trump, whose lawyers have said he did nothing wrong.