The U.S. House of Representatives has launched an official impeachment inquiry into President Donald Trump, accusing him of violating the Constitution by seeking foreign help to smear Democratic rival Joe Biden. The rarely used procedure is spelled out in Article II, Section 4 of the Constitution, which stipulates that the president and other officers of government “shall be removed from office on impeachment for, and conviction of, treason, bribery, or other high crimes and misdemeanours.”