The United States Senate officially opened the impeachment trial of President Donald Trump on Thursday. It marks only the third time the legislative body has held such a trial in U.S. history.

Chief Justice John Roberts of the Supreme Court was sworn in to preside over the trial. He then asked all senators to raise their right hands to take an oath to "do impartial justice according to the Constitution and laws, so help you God?"

The U.S. Constitution says the chief justice serves as the presiding officer in the trial. But only the 100 members of the Senate will pass judgement.

Earlier in the day, Democrats from the House of Representatives led by Adam Schiff read the charges, or articles of impeachment, in the Republican-led Senate.

"With the permission of the Senate, I will now read the articles of impeachment," said Schiff.

"House Resolution 755 Impeaching Donald John Trump, president of the United States, for high crimes and misdemeanors," Schiff began, reading the nine pages of the impeachment document.

Trump is charged by the House of Representatives with abuse of presidential power by pressuring Ukraine to investigate Democratic opponent Joe Biden. He is charged with withholding military aid to the country in exchange for an announcement of the investigation. Trump is also charged with blocking the Congressional investigation.

The president has repeatedly called the House impeachment hearing a "hoax." His administration has told its officials not to answer orders from the House for testimony and documents.

More accusations

Before the Senate met, the U.S. Government Accountability Office (GAO) said Thursday that the Trump administration had violated federal law in withholding military aid to Ukraine. It said, "The law does not permit the President to substitute his own policy priorities for those that Congress has enacted into law."

The GAO is an independent agency that reports to Congress.

On Wednesday, Schiff released new records from Lev Parnas about Trump's actions regarding Ukraine. Parnas was working with Trump's personal lawyer, Rudy Giuliani. Parnas has claimed that Trump knew of his efforts to find information that could hurt his political opponent.

House Speaker Nancy Pelosi, a Democrat, said the new information shows the need for the Senate to consider additional evidence about the president's actions toward Ukraine. She suggested that a special government lawyer could investigate the issue.

A quick end to the trial?

The president has suggested that he would be open to a quick vote to simply dismiss the charges.

Last December, Republican Senate Majority Leader Mitch McConnell told reporters that impeachment is a political process and not a judicial process.

"The House made a partisan political decision to impeach," he said. "I would anticipate we will have a largely partisan outcome in the Senate. I'm not impartial about this at all."

Democrat lawmaker Adam Schiff told the Associated Press, "The challenge is to get a fair trial." He noted, "It shouldn't be a challenge — if the senators are really going to live up to their oath to be impartial, they'll want a fair trial."

Republicans control the U.S. Senate with a 53-47 majority. However, it takes 51 votes during the trial to approve changes to the rules or to call witnesses. It also takes 51 votes to dismiss the charges against Trump.

Several Republican senators, including Susan Collins of Maine, Mitt Romney of Utah, Lisa Murkowski of Alaska and Lamar Alexander of Tennessee want to hear from more witnesses during the trial.

Romney said he wants to hear from former national security advisor John Bolton. Several witnesses have said Bolton was worried about the actions of Giuliani, the president's personal lawyer, in Ukraine

Opening arguments are to begin next Tuesday after the Martin Luther King Jr. holiday.

The historic trial will be a test of the Trump presidency as he is running for re-election. It also is expected to be a test of the nation's three branches of power and its constitutional system of checks and balances.

I'm Mario Ritter.

Hai Do adapted this story for VOA Learning English based on reports from the AP. Mario Ritter, Jr. was the editor.