Steve Richards: Can Blair recover his authority after these setbacks?

The ambiguity of Mr Blunkett's resignation symbolises his own peculiarly wrecked career and the enigma of Tony Blair's final years in Downing Street. Did he resign or was he sacked? Mr Blunkett insisted he resigned voluntarily. At a highly charged Prime Minister's Questions, Mr Blair declared that Mr Blunkett had "no stain of impropriety".

Mr Blair is left in the contorted position of losing a minister while protesting his innocence. Yet a source close to Mr Blunkett told me at around 9am yesterday morning that the minister was determined to address a scheduled meeting with a parliamentary committee, at which Mr Blunkett would prove he was up to the job. It is quite a leap from an assertion of ministerial authority to a voluntary resignation from the Cabinet within half an hour.

Mr Blunkett's second resignation is traced directly to his affair with Kimberly Quinn. Even after the relationship lapsed into vindictive acrimony, Mr Blunkett referred to her longingly as "Kimberly". Determined, single-minded and yet easily intoxicated, Mr Blunkett sought to do a few favours for her as Home Secretary. It cost him his job last December. Seeking ways to finance subsequent legal battles has led to a second fall.

But Mr Blunkett's tragic course can be traced further back to a fundamental political judgement made long ago. In the late 1980s he displayed a dramatic and pivotal loyalty to Neil Kinnock, as the Labour leader set about reforming the party. Mr Blunkett was the star of his party at the time and the key figure on the left. Without his support, Mr Kinnock would not have prevailed in his project to modernise the Labour Party. From that moment on Mr Blunkett became wholly loyal to the leader of his party, whoever the leader happened to be. He was an ardent Kinnockite who became a passionate supporter of John Smith and then finally the cabinet minister that delivered for Mr Blair.

Since 1997 he has basked in the glow of Mr Blair's approval, but this has led to a disastrous complacency on other fronts. Evidently, he felt free to criticise cabinet colleagues and take a casual approach to the ill-defined rules that govern ministerial conduct. He supported the leader and the leader supported him. This was the dynamic that mattered to him.

It was in this context that Mr Blunkett made the most fatal misjudgement of the lot, criticising cabinet ministers to his biographer. Last December, in advance of his first resignation, few ministers leapt to his support. They have been even less helpful this time. Mr Blunkett was dependent on his relationship with the leader. At the beginning of the week Mr Blair had his doubts and could not fully disguise them when making public comments.

By yesterday morning those doubts were greater still. For some days he knew where this story was leading. The much bigger political issue is whether the latest ministerial resignation undermines Mr Blair's authority. It was Mr Blair who brought Mr Blunkett back to the Cabinet a few months after his first resignation and at a time when the returning minister was still in emotional turmoil. More immediately, Mr Blair has suffered a sequence of events eerily familiar with the dying days of John Major's administration. First, Mr Blair unequivocally supported his cabinet minister. Now he has lost that minister.

If these events had happened in the first two terms Mr Blair would have strode on unharmed. In each case, his actions can be justified. After the election, few criticised the return of the widely liked Mr Blunkett. More immediately, Mr Blair made a judgement about the gravity of Mr Blunkett's misdemeanours and decided they were not worthy of destroying the ministerial career of a remarkable political figure. Mr Blunkett made a single mistake revealed in last weekend's The Independent on Sunday. He failed to consult the Advisory Committee on Business Appointments, a procedural oversight. It is a relatively minor offence. Even so, it follows the minor misdemeanours that arose when he lost his job last December. There is a limit to the number of minor offences a cabinet minister can commit. He had no choice but to go.

The context is more important than the details. At a point when ministers and MPs contemplate a future with a new leader, Mr Blair seeks to assert his authority on a range of policy fronts. The supreme test for Mr Blair's authority is not his handling of a cabinet reshuffle. He retains the powers of patronage and moved quickly yesterday to replace Mr Blunkett with John Hutton, an articulate and committed ally. But can he get his reforms through Parliament? This is his big challenge.

Mr Blair poses a different test for some in the Labour Party. Are the Cabinet and MPs ready to support reforms or leave valuable political space for a revived Conservative Party? Yesterday's vote on the anti-terrorist proposals suggests that Labour MPs are failing Mr Blair's test. It also suggests they plan to make it very difficult for Mr Blair to pass his.

Next month the Government plans to publish its latest reforms for the NHS, a moment of growing significance. The resignation of Mr Blunkett does not leave Mr Blair as a lame-duck Prime Minister. But, if he cannot get his reforms through Parliament, he will be more than lame. The Blair era will be over.