Substantial trial proceedings, however, will not begin until January 21, reports Efe news.

The chairman of the House of Representatives' Intelligence Committee, Adam Schiff, who will head a group of seven House managers prosecuting the case, was on Thursday tasked with reading the two articles of impeachment to the members of the Senate.

Supreme Court Chief Justice John Roberts was sworn in to oversee the impeachment trial.

He then proceeded to swear in all 100 senators - 53 Republicans, 45 Democrats and two independents (who caucus with the Democrats) - as jurors for the proceedings.

The first charge of "abuse of power" states that Trump used the power of his office to solicit "the interference of a foreign government, Ukraine, in the 2020 US presidential election".

That accusation stems from an allegation that during a phone call last July Trump sought personal political gain by improperly pressuring Ukrainian President Volodymyr Zelensky to publicly announce an investigation into the alleged interference years ago of US former Vice President Joe Biden, a leading contender for the 2020 Democratic presidential nomination, in a probe of his son Hunter's business dealings in Ukraine.

The House of Representatives found that Trump also improperly pushed Ukraine to publicly announce an investigation into a "discredited theory promoted by Russia alleging that Ukraine - rather than Russia - interfered in the 2016 United States presidential election."

It has also alleged that Trump exerted pressure by freezing nearly $400 million of US military and security aid to Ukraine about a week before he talked to Zelensky and delaying a head of state meeting between the two leaders at the White House.

Trump, who says the aid, eventually released on September 11, 2019, was withheld due to his frustration with what he considered to be an insufficient amount of monetary assistance provided to Ukraine by other countries, says the rough transcript of the phone call that the White House released on September 25 shows he did nothing wrong.

The second article of impeachment accuses the President of "obstruction of Congress", for directing executive branch agencies, offices and officials not to comply with subpoenas seeking documents and testimony deemed vital to the House's inquiry.

House Speaker Nancy Pelosi had delayed sending over the charges under the argument that she first needed to know what rules would govern the Senate trial.

Democrats say a fair trial can only be assured if the senators, who will act as jury in the impeachment case, hear from witnesses who did not testify during the proceedings in the House. It still remains to be seen whether 51 senators will vote to do so.

Since the approval of the impeachment articles, Senate Majority Leader Mitch McConnell has proposed a procedure modelled on the one the Senate followed in 1998 during the impeachment of Democratic President Bill Clinton.

Trump is the third US president to be impeached.

Both Andrew Johnson and Clinton were acquitted in the Senate, while Richard Nixon resigned in 1974 before the lower house could vote on his impeachment.

Under the Constitution, the approval of articles of impeachment in the House is to be followed by a trial in the Senate, where it takes a two-thirds majority to remove the president from office.

Due to Republicans' control of that upper chamber, a conviction is considered highly unlikely.