• Video report by ITV News Washington Correspondent Robert Moore

This was always going to be blockbuster testimony in the impeachment probe. And it has lived up to - and dramatically exceeded - the Democrats’ expectations.

Or to put it another way, this is the White House’s greatest nightmare playing out in real time on every network in America.

Ambassador Gordon Sondland is the man who is delivering the goods. He has drawn a bright line all the way from the murky arms-for-investigations business in Ukraine straight to the door of the Oval Office.

Five words are echoing around Washington, uttered in Sondland’s opening statements: “We followed the President’s orders.”

They will go down in history, surely, just like the famous Watergate question about Nixon: “What did he know and when did he know it?”

In the impeachment investigation there has been a missing link until this moment - no one has definitively tied the scandal directly to President Trump.

We knew that at one point $400 million worth of weaponry was being held back until Ukraine had ordered a corruption investigation into the son of Joe Biden. Hunter Biden was on the board of an Ukrainian oil company.

But there was always the possibility - until today (Wednesday) - that the arms deal had been held up by a freelancing Rudy Giuliani, the President’s personal lawyer, or by other rogue US actors.

Sondland’s testimony destroys that possibility. Trump is now the conspirator-in-chief who drove the attempt to wound a political opponent by withholding a Congress-authorised arms deal to a nation engaged in a simmering war with Russia.

It may not lead to the end of Trump’s presidency. He’s astoundingly resilient and the loyalty of republican senators - who will decide his fate - is still steadfast.

But this is still devastating to the President, and it’s not over yet.