The overlap between that effort and the president’s official foreign policy toward Ukraine is at the center of an impeachment inquiry. Here’s a timeline of events since January.

Details: Mr. Trump was driven to seek proof that the meddling in the 2016 election was linked to Ukraine and forces hostile to him, even fixating on a fringe conspiracy theory suggesting that Hillary Clinton’s missing emails might be found there. And Mr. Giuliani, backed by his boss, sought to tar former Vice President Joe Biden with unsubstantiated accusations.

What’s next? House Democrats’ first subpoena, issued Friday, gives Secretary of State Mike Pompeo one week to produce documents related to the inquiry. And Mr. Trump’s special envoy for Ukraine, who resigned last week, is expected to be interviewed by House leaders on Friday. The whistle-blower may testify soon.

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