It has been a terrible week for the Tories, and a very good one for the opposition.
The Tories expected to write a script for Jeremy Corbyn's Labour: incompetence and extremism. Yet as they review the wreckage of their week of tax credits chaos they must surely know this is not going to plan. They are now more out of touch with the British people than the unelected House of Lords.
Tory chaos over tax credits did not happen by accident. The Corbyn-led Labour Party made a political choice to resist the temptation to put constitutional practice ahead of the interests of millions of working people. Our leadership debate showed people wanted a strong, principled opposition on issues like this. Corbyn has channelled that from his leadership campaign through to Labour's Parliamentary tactics. The tactics flowed from the strategy of standing up to the government more clearly.
Corbyn has slowly but surely prodded away at the tax credits in PMQs week after week, gradually cornering the PM. His use of crowd-sourced questions - such as the case of Kelly - has isolated the Prime Minister from mainstream opinion.
Corbyn's leadership is interesting not just for how he has given expression to the need for a strong opposition in parliament. The changes go far wider. The balance sheet is growing.
Labour is now unafraid to connect with the mass movements and civil society that form our country's wider opposition to the Conservatives. The new leader's first act as leader was to address a refugee rally in Parliament Square. He dispensed with convention by speaking in Manchester during the Tory conference in support of the Communication Workers Union's case on Royal Mail. He gave a clearly pro-trade union speech to TUC in his first week as leader that showed he was not going to be pushed around by the Conservatives over Labour's relationship to the wider labour movement. A bolder attitude to the labour movement blunts the Tories' attack on the trade unions.
Labour's line on rail has been overhauled. It would be easy to forget the significance of this. Where we previously allowed for the possibility of the public sector challenging to run lines, we now clearly stand for the public sector to take on franchises as they expire. Instead of whether, we are now discussing how.
By putting the question of steel on the agenda during the state visit of the Chinese President, Corbyn forced Cameron to follow.
By taking up the case of Ali Mohammed al-Nimr, who has been sentenced to crucifixion, during Labour's conference, Corbyn again forced Cameron to follow. The extent of Corbyn's victory is shown by the Saudi Ambassador's complaint that Labour's leader had scuppered the squalid Saudi prison.
Under Corbyn the Labour party voted unequivocally against the immigration bill, refusing to be caught in a mire of triangulation. This in itself was a major and welcome shift in approach.
On Syria, Corbyn has been patient, set out the case for a political solution rather than a military one, and has currently put the ball back in the government's court.
On Scotland, Corbyn has quickly broken out of the damaging cycle of UK Labour leaders treading carefully about even visiting Scotland. Instead he has made visits to Scotland a regular part of his activities. His anti-austerity position is a welcome contribution to Scottish political debate.
By appointing a Shadow Cabinet that is genuinely broad Jeremy Corbyn has also changed how we as a party see ourselves. Jon Trickett, one of the left voices in the previous Shadow Cabinet, now heads a big spending department and leads on the constitutional convention. Senior appointments such as John McDonnell - alongside other new faces and those more traditionally seen as being to the right - are a major change that provides the building blocks for unity in action.
Jeremy Corbyn has only been the leader of the Labour party for a few weeks but he has already delivered significant change in how politics is conducted and in the direction of travel of the Labour party. It would be easy, in the light of the froth and noise of minor controversies, to lose sight of just how profound the change has already been.