Cue horror and anger. The Bishop of Oxford has attacked such vilification, particularly where it "draws on satanic imagery". And Peter Mandelson, sensitive and retiring campaign manager for Labour, writing in yesterday's London Evening Standard, described the poster as a "new low in propaganda ... [which] will disgust everyone ... a crass, clumsy move". Mr Mandelson believes that the message will backfire because "Tony Blair is a practising Christian, and by any standard a man of decency and integrity". Mr Mandelson is clearly right about Mr Blair's character, though he should remember (our tongue is a little in cheek, here) that the Spanish Inquisition was entirely run by practising Christians.
Mr Mandelson's protestations that such negative campaigning will backfire upon the Conservatives are tinged by more than a little nervousness. Having failed in its attempts to suggest that Mr Blair is old Labour in disguise, Tory Central Office is clearly enjoying more success in its contention that much of the danger of new Labour lies precisely in its newness. Who knows, it seems to ask, exactly where new Labour will take us? The poster itself is merely a way of exploiting the Clare Short debacle, while reminding the nation of the central anti-Labour theme of Conservative propaganda.
It is certainly the case that the speed of Conservative reaction to the Short interview marks the fact that we are now - semi-officially - living through an election campaign. It has begun, and nothing that happens will be judged by political commentators and politicians on any merits except whether or not it gains votes. But the Blair poster also raises the question of what kind of campaign it will be. Should the rest of us be as worried by it as the Bishop and Mr Mandelson are? Does this poster indeed mark the beginning of a prolonged and unprecedented nastiness, as some have begun to fear? And is it possible for a British election to be won or lost on the basis of wholly artificial fears, created with the same attention to real events as the average low-budget rented video?
If one steps back and takes a cool look at the Blair poster, it is hard to see why this is any more objectionable in principle than, say, an advertisement containing an entirely fictitious assertion about the tax implications of Labour policy.
The recent Tory party election broadcast likewise contained a statement about Labour policy on the treatment of criminals that was a straightforward and blatant untruth. In its distancing from any kind of factual argument the red-eye poster was, if anything, less offensive - it is not a lie, but an interesting joke. We surely need to be much more worried about the parties telling barefaced fibs about each other.
Moreover, propaganda must strike a chord if it is to succeed. It is completely fair for the Tories to suggest that an incoming and inexperienced Labour administration might cause damage to the perfectly united nation and roaring economy that Conservatives have striven so hard over 17 years to construct, just as it is for Blair's party to capitalise on an almost terminal weariness with the exhausted husks who currently occupy the corridors of power. What is unlikely to work is a campaign that runs contrary to the electorate's perception. Mr Blair is an improbable Beelzebub, as - for different reasons - is Mr Major.
So here is the real challenge for both of the two largest parties: Labour must explain to us how its new policies will work, simultaneously reassuring us and enthusing us - no mean feat. For their part the Conservatives must persuade us that there is a real reason why they should be given yet another term in office. And it must be said that, of the two tasks, Labour's is marginally the easier - only marginally, mind. As yet we know far more about what Labour plans to do in office, than we have been told about what will happen in a fifth successive Tory administration.
This is no accident. For all its confusions, Labour has broadly decided what kind of party it wants to be - though it hasn't fully grasped the implications of its own journey, and much can still go wrong. The Tories, however, stand on the threshold of their own ideological upheaval. A substantial and dynamic section of the party wants a thoroughgoing renewal of message and mission, but feel that such a change cannot easily be accomplished while still clinging to the reins of government. It has become very hard for Mr Major to propose great radical acts of government which satisfy all parts of his party, but almost as impossible for him to settle back on a "safety first" strategy. And that is why, though we can expect, for the moment, an unusually literal representation of the old adage "better the devil you know", the debate will shift soon enough onto whether or not you can trust Labour, or whether you can bear another bout of new Toryism. It may well be that posters from either side will play only a very small role in making up our minds on those questions.