U.S. House of Representatives Speaker Nancy Pelosi called Donald Trump an ongoing threat to 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, reports Reuters.

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.

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.

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 favor and Republicans opposed.

“If we do not act now, we would be derelict in our duty. It is tragic that the president’s reckless actions make impeachment necessary,” Pelosi added.

The vote would set the stage for a trial expected next month in the U.S. Senate on whether to convict Trump and remove him from office. While the House twice previously has voted to impeach presidents - Bill Clinton in 1998 and Andrew Johnson in 1868 - no president has ever been removed from office via impeachment.