Even before Mr Blair's coronation, the Lib Dems' relatively poor showing in the European elections suggested that disaffected Tories might be inclined to hurdle straight into Labour's arms. Now, with Mr Blair comfortably installed, the crisis for Mr Ashdown seems to be mounting. Latest opinion polls indicate a slump in Liberal Democrat support and in Mr Ashdown's own ratings. To add to his difficulties, the three members of the SDP-founding Gang of Four, who forced through merger with the Liberals seven years ago, have rushed to join the lionising of Mr Blair.
While it is true that Roy Jenkins, Shirley Williams and Bill Rodgers have never made a fetish out of loyalty to the leaders of whichever party they have found themselves in, the indecent speed with which Mr Blair appears to have overtaken Mr Ashdown in their affections is as clear a danger signal as you could get. But is Mr Ashdown cast down? Not at all. He might be a trifle irritated by the public drooling over Mr Blair by senior members of his own party, but he is as excited as they are by what is happening in British politics.
Of course, to be leader of the Liberal Democrats demands a special sort of crazy optimism. But even if Mr Ashdown cannot function other than as a professional optimist, it does not automatically follow that he is in the grip of a delusion. I have always found him to be a sober and thoughtful analyst of his party's predicament. In the run-up to the last election, when many people convinced themselves that the most likely outcome was a minority Labour government, sustained by Liberal Democrat support, Mr Ashdown was always intensely wary.
He regarded the prospect of any coalition with Labour, however informal or limited, as a poisoned chalice. He believed that the differences in culture and outlook with Labour were so great that any collaboration would have been not only a miserable experience in itself, but carried with it the certainty of alienating a substantial proportion of the Liberal Democrats' electoral franchise.
The reason for Mr Ashdown's excitement now is not hard to understand. Because he knows his party can never win an election on its own, his role has been to work for and wait for the conditions that might bring about the fundamental realignment that radicals of the centre and centre-left have dreamt of for more than 30 years. Whatever the short-term threat posed by Mr Blair's leadership, he reasons, his election makes infinitely more likely the essential pre-condition for realignment - a modernised and electable Labour Party.
Mr Ashdown makes no attempt to hide his high personal regard for the new Labour leader, and on more than one occasion has admitted that he would be hard-pressed to identify any great issues that would divide them. Quite how he sees their relationship developing is left vague. But if the opportunity presents itself, Mr Ashdown anticipates that with someone as like-minded as Mr Blair he could have a 'conversation' as opposed to a negotiation.
On a practical level, this means several things. First of all, Lib Dem tacticians are not nearly so dismayed by the polls as one might think. Labour is not suddenly going to replace the Lib Dems as the second-place party in Tory-held marginals across the south of England. To an extent not always realised, Labour has only a vestigial existence in the south outside London. In the bizarre super-constituencies of the European parliament elections, tactical voting was virtually non-existent, which did the Lib Dems no favours. At the next general election a Labour Party which does not scare middle-class voters could be the key to a Lib Dem breakthrough in many more seats.
Because of the electoral mountain Labour still has to climb (made that much steeper by the boundary changes), even a strong performance may leave it needing Lib Dem support in the House of Commons. But this time, assuming that the Blairisation of Labour is pursued with vigour over the next two years, the Liberal Democrats could offer their support on the basis of principled partnership. Given that Mr Blair is committed to holding a referendum on electoral reform, all that might cause a problem would be a Labour campaign in favour of rejection - but that would probably not be a deal-breaker.
For the time being however, Mr Ashdown reckons that the priority is to give his party a far sharper policy focus. He is acutely aware that Mr Blair is not the only one leading a party which continues to drag a fair amount of very shabby old baggage around with it. While the Liberal Democrats score well on foreign affairs (particularly on Bosnia, which has shown Mr Ashdown at his best), the environment and constitutional issues, it has been pretty feeble on health, education and the economy. As far as health and education are concerned, Mr Ashdown wants his reshuffled Commons team to start striking a much more authentically social market note.
But it is on economic issues that he hopes the contrast with Labour will be greatest. Whereas Mr Blair, under the influence of Gordon Brown, is determined to avoid a repetition of the over-specific tax and spending commitments which helped to lose Labour the last election, the Lib Dems will produce a fully-costed programme, in part paid for by a range of earmarked taxes. Mr Ashdown also wants to see much greater stress on competition and opportunity. In the circumstances in which he finds himself, the Liberal Democrat leader is making all the right moves.
Whether it will make any difference is another matter. At the speed with which Mr Blair is travelling, Mr Ashdown is going to find it very difficult to succeed in his aim of keeping intellectually five years ahead of Labour. That does not mean that the Lib Dems may not do quite well at the next election, hugely helped by the absence of any great Labour fear factor. But if Tony Blair manages to turn Labour into a party of the radical and progressive centre - a post-socialist party for a post-socialist age - it is hard to see why anyone should vote Lib Dem except for tactical or tribal reasons.
Mr Ashdown is right to see the apotheosis of Mr Blair as the catalyst for the long-awaited realignment of British politics, but it is at least possible that his party has already served its historic purpose in bringing it about.