US House Speaker Nancy Pelosi said on Wednesday President Donald Trump posed an "ongoing threat" to the country's security that left Democrats "no choice" but to impeach him."It is tragic that the president's reckless actions make impeachment necessary. He gave us no choice," said Pelosi, launching debate in the House of Representatives on impeaching the US leader."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," she said.