Trump is boycotting the hearing held by the House of Representatives Judiciary Committee, refusing to send his lawyers to participate in the proceedings, which he has called a "hoax".
Opening the hearing, Committee Chair Jerry Nadler said, "The evidence shows that Donald J. Trump, the President of the United States, has put himself before his country."
He accused Trump of endangering national security, using bribery and seeking foreign interference in US elections while dealing with Ukraine.
"Integrity of our elections is at stake," Nadler declared.
The Republican leader on the Judiciary Committee, Douglas Collins, said the Democrats had no case and were trying to impeach him only because they are afraid the Trump will win the 2020 elections because the economy is doing well.
He questioned the legitimacy of the impeachment process, saying the Democrats had decided soon after the 2016 election to impeach Trump and this was only an excuse.
Democrat Speaker Nancy Pelosi gave the OK last week for the Judiciary Committee to prepare the Articles of Impeachment which is a chargesheet against Trump that would be sent to the Senate for a formal trial with Supreme Court Chief Justice John Roberts.
The impeachment is sure to pass the Democrat-controlled House but action against Trump will fail at the Senate, where Republicans hold the majority, making the Democrat effort a campaign show highlighting what they say are Trump's misconducts.
Democrats plan to have the full House vote on impeachment next week before its Christmas vacation and Republican lawyer Steve Castor said the Democrats in their hurry rushed the process without due process.
After the opening statements, lawyers for the Democrats and Republicans took over the proceedings, making their cases for and against impeachment.
The hearing was a rehash of the testimonies and arguments over several weeks before the Judiciary and the Intelligence Committees.
Barry Berke, the Democrat lawyer, made a presentation that was like a documentary, playing excerpts from the testimonies as well as statements made by Trump before the media on related issues.
The Intelligence Committee released a report last week making the case of impeachment based on its hearings and the Republicans presented its own counter-report.
The impeachment stems from a phone call in July between Trump and Ukraine President Volodymyr Zelensky in which the US President requested as a "favour" an inquiry into the dealings of former Vice President Joe Biden and his son, Hunter, in that country.
Since Biden is a front-runner for the Democratic Party nomination to run against Trump, Nadler, Pelosi and others have accused Trump of seeking foreign interference in US elections.
Moreover, they have accused him of endangering US security by withholding about $400 million in military aid to Ukraine, a Washington ally, that is facing a war with Russia after its incursion into Crimea in order to force Zelensky to hold the probe.
This, they say, amounted to bribery.
Collins and other Republicans said the aid was released even though there was no Ukrainian inquiry into the Bidens and if it had a role in the hacking of Democratic Party-related computers before the 2016 elections.
Zelensky has also denied that he felt pressured by Trump.
Trump had sought an inquiry into Ukrainian gas company Burisma, which appointed Hunter Biden as a director with a monthly payment of $83,000, and the firing of a prosecutor looking into the company at the behest of Joe Biden.
Hunter Biden was removed from the Navy over drug allegations and had no experience in the energy industry or Ukraine.
Trump's personal lawyer Rudy Giuliani emerged during the hearings as a key figure in seeking Ukrainian investigations.
He has continued his controversial role by being in Ukraine last week, making inquiries.
Trump said over the weekend that Giuliani would present his findings to Attorney General William Barr and the Congress, further muddying the waters.
Republican Representatives led by Devin Nunes, their leader on the Intelligence Committee, staged a symbolic protest at the start of the hearings by occupying seats in the hearings chamber they were not permitted to occupy. The Democrats avoided a physical confrontation by not ordering them removed.
Later a right-wing talk show host tried to disrupt the hearing by screaming against the Democrats. He was removed by the police.
(Arul Louis can be contacted at arul.l@.in and followed on Twitter @arulouis)
( With inputs from IANS )