The people of Spain have given a mixed message to the rest of Europe. In the first referendum on the proposed new European Union constitution, the Yes side won by a huge majority - but only 42% of voters took part.
Mr Zapatero successfully led the battle for the constitution
European leaders with a stake in the acceptance of the EU constitution were quick to claim a victory from Spain's referendum vote on Sunday.
The President of the European Commission, Jose Manuel Barroso, declared the Spanish people had said "Yes to Europe, Yes to the future".
Javier Solana, who is in line to become the first EU foreign minister if the constitution becomes law, said that the vote in his native Spain would encourage a Yes vote in the nine other countries that are to hold referendums.
And French President Jacques Chirac, who could face difficulties winning the referendum which is planned in France, said the Spanish Yes "shows the path" to other countries which will follow.
Within hours of learning the result from Madrid, Mr Chirac's Minister for European Affairs, Claudie Haignere, said France could be ready to hold its referendum from early May.
Until now, June was seen as the most likely month for the French vote.
But many, including EU enthusiasts, have been dismayed by the lack of commitment shown by the people of Spain.
Turnout was only 42%, the lowest in any national vote in Spain since the restoration of democracy there more than 20 years ago.
Of the votes cast, 77% were for the EU constitution and only 17% against.
The No vote was stronger in some areas than others
But 6% of voters cast blank ballots, in apparent protest at being asked to approve an important and wide-ranging document which - polls show - most Europeans do not properly understand.
France's Foreign Minister Michel Barnier acknowledged that the Spanish vote had highlighted a challenge - that of mobilising voters and explaining the text of the constitution to citizens.
And Mariano Rajoy, leader of the Popular Party, which takes a more hard-headed view of the EU, mocked the Spanish government's boast that it would set an example to Europe. It turned out that "we are not a model of anything", he said.
Analysis of the Spanish vote gives clues about problems which may be magnified in other EU states.
Despite very large sums of EU aid spent on projects all over Spain, the No vote reached 28% in the national region of Catalonia - and fully one in every three votes in the Basque region, where local demands for independence have often turned violent.
The cooling of Spanish ardour for the EU may be due in part to their realisation that the bonanza of subsidies is soon to end, after the EU's enlargement to take in many poorer states to the east.
And it might be catching. In Portugal, which is to hold its own referendum at a later date, a commentary in the Publico newspaper has warned that voters might seek to make Europe a "scapegoat" for the nation's current problems.
So the message from Spain is a muffled one. The European Commission Vice-President, Margot Wallstrom from Sweden, hopes it will be "a signal of encouragement" to 220 million voters in the nine other EU states which are to decide the fate of the constitution in referendums still to come.
But in Britain, where public opinion is reckoned to be coolest of all towards the constitution, a dissident Labour MP who opposes it, Ian Davidson, cast doubt on that.
"If turnout doesn't even reach 50% in a country like Spain, what hope does Tony Blair have of enthusing voters here?" he asked.
The other EU countries expected to hold referendums on the constitution over the next 18 months are the Czech Republic, Denmark, France, Ireland, Luxembourg, the Netherlands, Poland, Portugal and the UK.