Several major revelations and egregious presidential action against the investigation later in 1973 prompted the House to commence an impeachment process against Nixon. The U.S. Supreme Court ruled that Nixon had to release the Oval Office tapes to government investigators. The tapes revealed that Nixon had conspired to cover up activities that took place after the break-in and had attempted to use federal officials to deflect the investigation. The House Judiciary Committee then approved articles of impeachment against Nixon for obstruction of justice, abuse of power, and contempt of Congress. With his complicity in the cover-up made public and his political support completely eroded, Nixon resigned from office on August 9, 1974. It is believed that, had he not done so, he would have been impeached by the House and removed from office by a trial in the Senate. He is the only U.S. president to have resigned from office. On September 8, 1974, Nixon's successor, Gerald Ford, pardoned him.