WASHINGTON (BLOOMBERG) - The House sent two articles of impeachment against Donald Trump to the Senate Wednesday (Jan 15) in a sombre procession of Democratic prosecutors - the first step to begin a trial that is all but certain to end in the president's acquittal.

Senate Majority Leader Mitch McConnell invited the seven House impeachment managers to return at 12pm on Thursday to read the articles aloud on the Senate floor. John Roberts, the chief justice of the US, will be sworn in at 2pm to preside over the trial. He will then swear in all 100 senators as jurors.

McConnell also said Trump will receive a formal summons to send his defence counsel, which will be the first time the White House will participate in the impeachment process. The trial, expected to last several weeks, will begin "in earnest" on Tuesday, McConnell said.

"This is a difficult time for our country, but this is precisely the kind of time for which the framers created the Senate," McConnell said, with the impeachment managers listening in the back of the chamber. "I'm confident this body can rise above short-termism and factional fever and serve the long-term best interests of our nation. We can do this, and we must."

Wednesday's historic but largely symbolic ceremony of impeachment managers marching two-by-two across the Capitol came after the House voted 228-193 to adopt the resolution naming the managers selected by Speaker Nancy Pelosi.

The seven Democratic lawmakers who will prosecute the House's case have already begun meeting to plan their strategy to present the charges of abuse of power and obstruction of Congress. Their pitch will be as much to the American people weighing the seriousness of the allegations against Trump, since it's all but inconceivable that at least 20 Republican senators would turn on the president to reach the two-thirds margin needed to remove him from office.

Intelligence Chairman Adam Schiff will lead the team, which consists of Judiciary Chairman Jerrold Nadler of New York, Zoe Lofgren of California, Hakeem Jeffries of New York, Val Demings of Florida, Jason Crow of Colorado and Sylvia Garcia of Texas.

Trump's defence will be led by White House Counsel Pat Cipollone and his personal attorney Jay Sekulow, according to people familiar with the matter. More people could be added to the team.

Wednesday's formal notification to the Senate ends a month-long stalemate between Pelosi and McConnell, who rebuffed Democratic demands to guarantee that new witnesses would be called for the trial. The Kentucky Republican, backed by his GOP majority, also refused to set out the trial procedures in advance.

Pelosi, Schiff and Nadler said Democrats will continue to fight for the introduction of new witnesses and evidence at the trial. McConnell has sought to engineer a swift proceeding that would quickly acquit the president. However, at least four Republican senators have said publicly that they want a chance to consider calling witnesses or viewing new evidence.

That decision, made on a simple majority vote, won't come until after the House managers and Trump's defence team have presented their cases and answered questions from senators.

Several of the newly appointed impeachment managers said on Wednesday that they hope senators will take their constitutional duty seriously.

"The Senate is on trial as well as the president," Nadler said.

As Pelosi was announcing the impeachment managers Wednesday morning, Trump taunted Democrats on Twitter.

Pelosi has come under fierce criticism from Trump and Republicans for delaying the resolution to send the articles of impeachment to the Senate. Since the Democratic majority in the House voted to impeach Trump last month, former National Security Adviser John Bolton offered to testify to the Senate under subpoena. His lawyer previously said that Bolton has information that wasn't part of the evidence gathered during the impeachment inquiry.

In addition, House impeachment investigators on Tuesday sent phone records and other new evidence obtained from a lawyer for Lev Parnas, an associate of Rudy Giuliani, to the Judiciary Committee as potential additional material for the Senate trial.

There were 13 Republican House managers in the 1999 impeachment case against then-President Bill Clinton. Two of those former managers said they recall feeling the pressure of the entire nation watching them.

"Be prepared and try not to screw it up," Representative Steve Chabot of Ohio, who is still on the Judiciary Committee, said in an interview. He said one of the things that a manager is always conscious of is that "a lot of people back home, as well as the nation, are watching." Former Representative Bill McCollum of Florida said it's a serious matter and his advice to the managers is they must "purport yourself accordingly. Do your very best job." The two men, both lawyers, said preparation for the Senate trial began almost immediately for the House managers, working under then-Judiciary Chairman Henry Hyde of Illinois.

They divided the workload, and Chabot said one of his assignments was to study the history of perjury. One of McCollum's assignments was to prepare witness testimony for the Senate trial.

McCollum's second role was helping tie the proof of the case together in a summary presentation and delivering what amounted to some of the closing arguments of the case.

Chabot said that while this role was one of the most "notable" points of his congressional career, "impeachments in general are low points for our country."