Democrats, who need to make their case to an American public that polls show to be bitterly divided on the issue, concluded in a 300-page report by the House Intelligence Committee on Tuesday that Trump solicited Ukraine to undertake investigations that would benefit him politically.
Trump "directly and explicitly invited foreign interference in our elections", said House Judiciary Committee Chair Jerry Nadler, referring to Trump's effort to get dirt on his Democratic rivals from Ukraine.
The House Judiciary Committee is weighing findings by fellow lawmakers that Trump misused the power of his office for personal political gain and then obstructed Congress' investigation as possible grounds for impeachment.
Based on two months of investigation sparked by a still-anonymous government whistleblower's complaint, the Intelligence Committee's Trump-Ukraine Impeachment Inquiry Report relies heavily on testimony from current and former USA officials who defied White House orders and appeared. "Chairman Schiff's report reads like the ramblings of a basement blogger straining to prove something when there is evidence of nothing".
Gerhardt, who specializes in the legal relationship between Congress and the President and may be the most influential expert of the subject of presidential impeachments, also spends a significant portion of his statement unfavorably comparing Trump's actions to the conduct that led former president Richard Nixon to resign from office in disgrace.
"You just don't like the guy", said Rep. Doug Collins of Georgia, the top Republican on the panel.
None of that will come as a surprise to Mr Trump or members of his Republican party - but it will infuriate the president, our correspondent adds. "I learned nothing from Adam Schiff. I think Adam Schiff is a deranged human being".
"They have also challenged the very core of our Constitutional system of checks and balances, separation of powers, and rule of law", the Democrats said.
The session in the U.S. house will delve into possible impeachable offences, but the real focus will be on the panel, led by chairman Jerrold Nadler, and made up of a sometimes boisterous, sharply partisan division of members of congress.
The first investigation Mr Trump wanted from Ukraine was into former Vice-President Joe Biden, his main Democratic challenger, and his son Hunter.
Lawmakers and the public have heard testimony from current and former officials that military aid was withheld from Ukraine and that a White House meeting with Zelenskiy was conditioned on Kiev announcing a probe into Biden, as well as one into a debunked conspiracy theory about Ukrainian interference in the 2016 USA election.
Traveling with Trump in London for a meeting of North Atlantic Treaty Organisation leaders, Stephanie Grisham, the White House press secretary, denounced the Democratic report moments after it was released.
Mr Trump has denied any wrongdoing.
Now that the report on the from the House Intelligence Committee is public, the focus is turning to the House Judiciary Committee - which will decide whether or not to put the articles of impeachment against U.S. President Donald Trump to a vote after conducting its own hearings.
"President Trump and his senior officials may see nothing wrong with using the power of the office of the president to pressure a foreign country to help the president's reelection campaign", it said. House leaders announced they would remain in session until December 20, more than a week longer than initially planned, leaving open the possibility of a vote to impeach Trump days before Christmas.
One of the scholars told Wednesday's hearing that Trump had perpetrated one of the gravest political transgressions in USA history. Trump's counsel said this week that he won't participate in the Judiciary Committee's first hearing, calling it "unfair".
But conviction can only happen in the Senate and requires at least two-thirds of its members, or 67 senators, to vote in favor. Currently, the Senate has 53 Republicans, 45 Democrats and two independents.