Speaker Nancy Pelosi announced the opening of a formal impeachment inquiry into President Donald Trump saying he betrayed his oath of office to hurt Democratic rival Joe Biden.

The move has set up a dramatic constitutional clash 14 months before the presidential election.

‘Today I'm announcing the House of Representatives is moving forward with an official impeachment inquiry,’ Pelosi said in a news conference.

She pointed out that the actions of the Trump presidency revealed the dishonorable facts of the president’s betrayal of the integrity of our elections.

 The inquiry marks just the fourth time in American history a president has faced a viable threat of impeachment.

The speaker has long resisted calls from many progressive lawmakers to initiate impeachment proceedings against the president, but Democrats appear to have reached a breaking point over the administration's refusal to hand over a whistle blower complaint related to Mr. Trump's interaction with a foreign leader.

‘This week, the president has admitted to asking the president of Ukraine to take actions which would benefit him politically,’ Pelosi said

The current furor stems from a call Mr. Trump made to the president of Ukraine in July, in which he admitted discussing Joe Biden in the context of fighting "corruption" in the country.

 Mr. Trump and his allies, in particular personal attorney Rudy Giuliani, have accused Biden of pushing for the ouster of a Ukrainian prosecutor while he was vice president in order to benefit his son. The prosecutor was widely seen as corrupt, and no evidence of wrongdoing by Biden has emerged.

Mr. Trump, who is in New York for the United Nations General Assembly, reacted angrily to Pelosi's statement, calling it a "total Witch Hunt!"

Earlier in the day he said he would release the transcript of the call with Ukrain President Volodymyr Zelensky that is part of the whistleblower complaint.