The first big hurdle is the local elections on 5 May. The outcome will not cheer the Tories; in the shire counties, district councils could fall to the Liberal Democrats; in London at least two boroughs could fall to Labour.
On the other hand, Labour won seats in the 1990 elections - for example in the North-west - which were never properly theirs. They won them at the height of Margaret Thatcher's personal unpopularity and when the poll tax was an issue.
In other words, Labour starts in some parts of the country from an artificially high base and could make fewer gains than the opinion polls would suggest. There is therefore some room for believing that Mr Major could absorb the shock of the local elections.
More crucial is the Eastleigh by- election - for which there is no good time for the Tories to move the writ - and the European elections, the first since those which in 1989 began the slide for Mr Major's predecessor, on 9 June.
The Tory high command's current plan is that Mr Major will adopt a much higher profile than Baroness Thatcher did then. That strategy may help the campaign - but it also runs the risk of associating him more closely with what seems certain to be some defeats.
In 1989, the Tories took a 32 per cent share of the vote. Most current polling puts them at about 28 per cent. After Euro-polling day there could well be a weekend of frenzied speculation about the leadership - based, oddly, not on the results but on a mixture of exit polls and, if it takes place on that day, on the result of Eastleigh. It's not surprising that the timing of Eastleigh is delicate; anything earlier than 9 June gives the Liberal Democrats a platform to build a bandwagon for the European elections. If it is on 9 June, then it could deprive Mr Major of some alibis for the Euro-losses - for example low turn-out.
This is certainly a period of danger for Mr Major. It is always possible that 'the suits' - Sir Marcus Fox, chairman of the 1922 Committee; Richard Ryder, the chief whip, and others could knock menacingly on his door. But let's suppose not. Mr Major still has to decide whether to have a reshuffle to refresh his government. He could even try a 'night of the long knives', as Harold Macmillan did in 1962. And it is fraught with dangers; sacking any of the Cabinet ministers who expressed their dissent over the European voting compromise, for example, would create a powerful new focus of hostility on the right of the party.
Suppose he does manage a successful reshuffle, there is a relatively peaceful end to the session and everyone goes off on their summer holidays. What is still to come? First is the Scott inquiry which could claim more scalps, or at least further tarnish the Government's image. And there are two crucial votes on the critically divisive issue of Europe. One is on 'Own Resources' - which means an increase in European Union budget contributions and the other, ie enlargement, the very issue at the heart of the row which has just destabilised Mr Major. On the first vote, he could still probably force it through with backing from Labour and the Liberal Democrats. On the second there is the possibility at least that Labour will try to link support to the social chapter precipitating a second Maastricht-style crisis.
Finally, there is the November period, still the maximum moment of danger assuming Mr Major both toughs out his troubles and fails to stage a political comeback as some of his closest allies believe he could.
First, within 14 days of the Queen's Speech opening the new session, 10 per cent of the parliamentary party, or 34 MPs on current figures, have to write in confidence to sir Marcus saying there should be an election. Mr Major finds a proposer and seconder, then a challenger comes forward, who will have to declare the names publicly. And a contest is under way.