U.S. President Donald Trump has said that this week he will publish a transcript of the first telephone conversation with Ukrainian President Volodymyr Zelensky.
The inquiry into whether Trump misused US foreign policy to ask Ukraine to target a domestic political opponent enters a critical phase on Wednesday when Congress holds its first public, televised hearings to question witnesses.
The transcript is from a call with Zelenskiy after the Ukrainian was elected president but before he took office.
He has been walking a diplomatic tightrope to maintain good relations with both US political sides whose bipartisan support Ukraine counts on for aid and diplomatic cover against Russian Federation following Moscow's annexation of the Crimea peninsula in 2014.
Trump contends the transcript of his call with Ukraine's president was "perfect". None has been removed from office, although Richard Nixon resigned as he faced nearly certain impeachment in 1974 over the Watergate scandal.
Democrats, who control the House, have argued that Trump abused his power in pressing a vulnerable U.S. ally to carry out investigations that would benefit Trump politically.
At Wednesday's hearing you can expect republicans to argue that President Trump did not lay out conditions when he asked Ukraine's president to launch political investigations, and Ukraine wasn't aware that aid would be withheld at the time of the July 25th phone call in question.
In her testimony, senior Pentagon official Laura Cooper detailed confusion and concern in the US national security community after Trump's White House blocked almost $400 million in security assistance to Ukraine without explanation.
House Speaker Nancy Pelosi announced in September that the House of Representatives would begin a formal impeachment inquiry into Trump.
If that occurs, the 100-seat Republican-controlled Senate would hold a trial, but Republicans have so far shown little interest in removing Trump from office.