There is no doubt that President Donald Trump's actions require him to be removed from office, three scholars of US constitutional law have testified.
The three experts described Mr Trump's efforts to solicit help from a foreign nation as a crime and accused him of obstructing justice.
Four experts, three picked by Democrats and one by the Republicans, have been testifying in Congress.
The fourth said Mr Trump's actions were wrong, but not impeachable.
As the investigation entered a new phase, the experts testified to the House Judiciary Committee which began hearings aimed at drawing up articles of impeachment.
Its hearings come hot on the heels of the House Intelligence Committee's investigation, which concluded on Tuesday with a 300-page report accusing Mr Trump of putting his own personal political interests "above the national interests of the United States" by soliciting foreign interference in the 2020 US elections.
The impeachment process began in September after an anonymous whistleblower complained to Congress about a July phone call by Mr Trump to the president of Ukraine, in which Mr Trump appeared to tie US military assistance to Ukraine launching investigations which would help him politically.
The White House has rejected the allegations made by Democrats, who hold the majority in the House of Representatives. Mr Trump questioned the patriotism of Democrats, asking: "Do they love our country?"
Among formal impeachment charges expected to be considered by the judiciary committee are abuse of power, obstruction of justice and contempt of Congress.
Democrats are keen to hold a vote on impeachment in the House of Representatives before the end of the year, with the prospect of a trial in the Senate perhaps as early as January 2020.
The four law professors questioned by the committee were:
Stanford University's Prof Pamela Karlan, Harvard University's Prof Noah Feldman and from the University of North Carolina, Prof Michael Gerhardt, chosen by the Democrats.
George Washington University's Jonathan Turley, picked by Republicans.
The legal experts interpreted the impeachment clause of the constitution, which allows for presidents to be removed from office due to "high crimes and misdemeanours".
Prof Feldman testified that the "evidence clearly constitutes" an impeachable offence because Mr Trump's interactions with Ukraine show him "corruptly using the powers of the presidency for personal political gain".