There could have been no more powerful a demonstration of the opposition Tony Blair faces from his own party over his plan to go to war on Iraq.
In a riveting resignation speech to MPs, former cabinet minister Robin Cook attempted a forensic, line-by-line demolition of the prime minister's case.
Most powerful resignation speech since Geoffrey Howe
And in an unprecedented show of support, his speech was greeted with a highly un-Parliamentary standing ovation and eruption of applause from a large number of Labour backbenchers.
The Commons has never seen anything quite like it and Speaker Michael Martin was forced to demand order as the extraordinary display showed no sign of abating.
This was more like an election speech or a conference performance than a resignation statement.
The prime minister, who was not in the chamber, may have felt the hairs on the back of his neck prickle as Mr Cook ended with a call for the Commons to stop the war with its vote on Tuesday night.
That will not happen. But the anti-war rebels have finally got what they have so far been lacking - a leader with the ability to scare the socks off the prime minister.
And any lingering hopes in Downing Street that the revolt may start to wane were blown away with this single, brief statement.
Incisive and devastating
Mr Cook is seen to have resigned without bitterness or ill-feeling and with his integrity and standing enhanced.
But he has put himself at the head of the anti-war movement and, in doing so, probably breathed new life into it.
He voiced his support for the prime minister's efforts in seeking a second resolution.
But he then went on to set out in the clearest and most comprehensive way yet all the strands of opposition to the government's policy.
It was the most powerful resignation speech since Sir Geoffrey Howe's famous performance which set the seal on Margaret Thatcher's future.
If anything, it outdid even that. Mr Cook has long been viewed as one of the most incisive and devastating Commons performers.
And on Monday night, as he ended a 20-year ministerial career, he brought all his qualities into sharp focus.
Mr Blair has every reason to be very scared indeed.