But what happened in the Commons yesterday was much more than a technical defeat on a single amendment. For a start, this was no defeat by a whisker. In parliamentary terms, it was a humdinger of a defeat, with 49 Labour MPs rejecting the 90-day detention period. The panic measures that had brought the Chancellor back from Israel, the Foreign Secretary from Moscow, and the Armed Forces minister from his hospital bed, were utterly futile. Without them, the Government would still have lost the vote. The margin, and the message, were clear.
Most of all, though, this was a devastating personal defeat for Tony Blair. The 90-day issue had become a test of the Prime Minister's authority, less because there was any principled difference between 90 or 28 days than because Mr Blair had insisted on 90. That so many Labour MPs nonetheless defied his pleas shows how his authority has been diminished. An adverse effect of this growing breach between the Prime Minister and his party will be the slowing of public sector reform.
In the past, Mr Blair's brinkmanship has always paid off. The spell is now broken. And it is broken not least because his judgement has been increasingly shown to be fallible. The decision not to seek a compromise before the debate was his and his alone. He went for broke, insisting that it was "sometimes better to lose and do the right thing than win and do the wrong thing". This was not only an arrogantly self-serving pronouncement before a parliamentary vote, but an exceptionally poor judgement call on his part - the culmination of the many poor judgements that have marked this ill-fated Bill.
Drafted in the wake of the terrorist attacks in London in July, the anti-terrorism Bill suggested a prime minister and a government driven not by high principle and competence but by fear. As many MPs argued yesterday, in a debate that showed Parliament at its best, such extended detention without charge threatened the very fundamentals of our judicial system and the civil liberties it guarantees. They noted - rightly - that neither the Prime Minister nor any other member of the Government had proved convincingly that the new provisions would enhance terrorist prevention.
They also resented the way in which the police, in the person of the Commissioner of the Metropolitan Police, Sir Ian Blair, and The Sun newspaper had been mobilised in the Government's support. The police, like the judiciary, must not only be above and beyond party politics, but unambiguously seen to be so. The key to preventing terrorism is reliable intelligence and skilled police work, not ever more repression.
But it was not only the Prime Minister's judgement on the anti-terrorism Bill that was called into question yesterday. Over the debate hung the dark shadow of Iraq and the "war on terror". Time and again, MPs asked why they should believe the arguments of the security services and the police when they had been so wrong about Iraq's weapons and had shot dead an innocent man at Stockwell. Where once Mr Blair would have been given the benefit of the doubt, his word is now a liability. This is a prime minister whose credibility, like his authority, is ebbing away, and Parliament - to the great credit of the MPs who yesterday followed their conscience - is coming back into its own.