Trump's impeachment hearing underway, Only 3 US presidents faced such hearing before

The United States House launched the first public hearing on Wednesday of Donald Trump's impeachment investigation, the extraordinary process to determine whether the 45th president of the US should be removed from office.

Rep Adam Schiff, the Democratic chairman of the House Intelligence Committee, opened the hearing for the start of testimony.

The moment is remarkable even for a White House full of them. The hearing is the first chance for America, and the rest of the world, to see and hear for themselves about Trump's actions toward Ukraine and consider whether they are, in fact, impeachable offenses.

From Capitol hill's packed hearing room the proceedings were being broadcast live, and on Social Media. Only three US presidents have faced such hearings before, and real-time Twitter commentary is expected from the president himself.

The narrative is splitting Americans so far, mostly along the same lines as Trump's unusual presidency. The Constitution sets a dramatic but vague bar for impeachment, and there's no consensus yet that Trump's actions at the heart of the inquiry meet the threshold of "high crimes and misdemeanors."

Trump calls the whole thing a "witch hunt".

Nancy Pelosi speaker of Democratic House was initially reluctant to launch a formal impeachment inquiry. But she pressed ahead in September after the whistleblower's Complaint.