House of Representatives speaker Nancy Pelosi has opened debate on the impeachment of President Donald Trump, arguing that his actions have left legislators with "no choice" but to act. Ms Pelosi said she opened debate "solemnly and sadly", insisting if the House does not act now, "we would be derelict in our duty". She said Mr Trump used his office to obtain an "improper political benefit" from Ukraine at the expense of the nation's security. She said the House was forced to add a second article of impeachment against the president, obstruction of Congress, because "never before in the history of our nation have we seen a president declare and act as he is above the law". After a day of debate, the House will vote on the two articles of impeachment against the Republican president later on Wednesday. The Republican-controlled Senate is expected to acquit him in a trial next year.