Impeachment proceedings against President Donald Trump formally began on Thursday. Supreme Court Chief Justice John Roberts was sworn in as a presiding officer, and the senators took an oath to be impartial jurors.

Donald Trump has become the third president in US history to be impeached after the House of Representatives voted Wednesday on two charges against him — abuse of power and obstruction of Congress.

The House passed the first charge, accusing Trump of abusing the power of his office, Wednesday evening on a 230–197 vote. The House then passed the second article of impeachment, obstruction of Congress, on a 229–198 vote.

The abuse of power article alleges that Trump pressured Ukraine to interfere in the 2020 election by withholding hundreds of millions of dollars in military aid unless the country’s president announced an investigation into former vice president Joe Biden and his family.

The obstruction of Congress article is tied to Trump directing executive branch agencies and officials not to comply with congressional subpoenas. Several administration officials subsequently refused to testify during impeachment proceedings.