US House of Representatives Speaker Nancy Pelosi called Donald Trump an ongoing threat to the American democracy as the bitterly divided chamber engaged in an impeachment debate before historic votes on two charges, accusing the Republican President of abusing his power and obstructing Congress.

The Democratic-controlled House launched a planned six hours of debate on the two articles of impeachment formal charges arising from the President’s actions toward Ukraine, with time equally divided between the parties and no amendments. Trump will become the third US President to be impeached.

“Today, we are here to defend democracy for the people,” Pelosi, the top Democrat in Congress, said in a speech on the House floor after reading the pledge of allegiance, drawing applause from lawmakers in her party. As the debate unfolded, Trump on Twitter called the Democratic-led proceedings “An Assault On America” and on his party.In a series of speeches on the House floor, Republicans defended the President and accused Democrats of seeking to topple him from power using an unfair and rigged process to nullify the results of the 2016 election.

Separate votes on the two charges are expected in the early evening. The votes are expected to fall almost entirely along party lines, with Democrats in favour and Republicans opposed.

“If we do not act now, we will be derelict in our duty. It is tragic that the President’s reckless actions make impeachment necessary,” Pelosi added. “He gave us no choice. What we are discussing today is the established fact that the President violated the Constitution. It is a matter of fact that the President is an ongoing threat to our national security and the integrity of our elections – the basis of our democracy,” Pelosi said.