For Mr Mitterrand, the stakes are high enough. The difference between a vote in favour of the Maastricht treaty on European union and a vote against it could decide whether he crowns his career with a triumphant retirement in 1995, or is forced ignominiously to leave the French presidency this year.
But for Mr Delors, who is 10 years younger than the septuagenarian Mr Mitterrand, the stakes are higher still. Unlike the President of France, he is not necessarily in his last job. Until the polls in France dipped against Maastricht, Mr Delors was set to lead the European Commission for another two years after his current term expires at the end of December, and then perhaps to hunt for something still bigger and better after 1994 - perhaps Mr Mitterrand's job.
This week, however, Mr Delors revealed a fear that any such ambitions may soon turn to dust. On Tuesday he said bluntly that he would feel unable to stay in Brussels past the end of 1992 if France says 'no' to Maastricht.
For one thing, said Mr Delors, a French President of the Commission would suffer a sharp loss of influence if his own country had turned its back on the cause of European union. For another, he would not know how to tackle the job of mending the porcelain of the shattered treaty. That, he insisted, was not work for someone who has 'fought so hard and invested so much' over the past seven years in the ideal of European union. It would be better left to an opponent of the treaty, someone who has ideas about what to replace it with.
A source who met Mr Delors on Wednesday was surprised at what a broken man he seemed. 'Delors walked like an old man; he was tired and evidently nervous and depressed.' And one of the president's own advisers said yesterday that he was 'absolutely certain' that the threat of resignation was sincere.
But there is a paradox behind Mr Delors' latest pronouncement. If the porcelain breaks as he fears, it will not be because of France but because of Denmark, which made the first crack when it rejected Maastricht in May.
The Danish referendum result was the biggest blow to confidence in the European Community for the past 20 years. After all the long hours they spent negotiating the Maastricht treaty last year, politicians and civil servants had come to believe that public support would come automatically. The fact that Denmark was known, along with Britain, as a reluctant European did not lessen the blow when the very first country set to ratify the treaty turned it down.
After Denmark's surprise 'no', the EC foreign ministers huddled in Helsinki and agreed that they would carry on with business as usual. They would win ratification from electorates and parliaments in the other 11 member states and then present the Danes with an offer they could not refuse: to reconsider, or leave the Community altogether. How else, said officials at the time, could the EC deal with 50,000 Danes who sought to stand between 330 million Europeans and their destiny?
In fact, the legal position was irrefutably clear, and remains so now. Before it can come into force, the treaty must be ratified by all 12 of the EC's member states. So even if France approves it, and the eight other countries that have still to ratify it do so too, it is still far from clear whether the treaty will ever come into force. The answer to that question can be found only in Denmark.
So whether France votes 'yes' is no longer the issue. This week's opinion polls have shown that even after all the domestic politics are excluded, there is clearly a substantial minority of French citizens who remain suspicious about the whole Maastricht enterprise. No matter whether they have misunderstood the treaty, as some Danes did; they are not willing to be railroaded into the politicians' arrangements for a new Europe.
A different calculation may therefore emerge for Mr Delors. If the French do the same as the Irish, and swing at the last minute towards supporting the treaty two to one, then the referendum can be claimed as a kick in the pants to propel the Maastricht treaty over Denmark's doubts. Mr Delors will then hope to stay in Brussels and resume the onward march of the greater Europe.
If, on the other hand, the French vote against the treaty, his position may be no worse. Mr Mitterrand will be under extreme pressure to resign; politicians all over Europe, terrified at the prospect of resurgent Franco-German tension, will claim that the French turned against their President rather than against their European ideals. And the French public itself, tinged with guilt at having scuppered Maastricht, would be looking for a new President to re-establish their European credentials.
Who better, then, than Brother Jacques to call to the Elysee? His term in Brussels would be the best possible passport and his popularity in the opinion polls earlier this summer shows that by staying out of Paris he has made himself one of France's most popular politicians.
But the worst possible outcome for Mr Delors is also the most likely. A narrow 'oui' to Maastricht from France will keep Mr Mitterrand in office, but will solve nothing at the European level. While Mr Mitterrand rejoices at the splits in the French right, Mr Delors will face a long cold winter trying to make sure Germany and Britain ratify the treaty - with Denmark nagging at him reproachfully like a sore tooth.Reuse content