Prodi is also head of the main Italian center-left opposition coalition. Writing in a leading Italian newspaper ("Corriere della Sera") on 27 March, he said that if his opposition grouping wins the next Italian parliamentary elections, it will withdraw Italy's 3,000 troops from Iraq.
In a hard-hitting rejection of the U.S.-led war, Prodi said the occupation is "not visibly capable of restoring peace and security in Iraq."
Prodi's comments come only a few weeks after the surprise win of the Socialists in the Spanish general elections, in the wake of the Madrid bombings.
Prime Minister-designate Jose Luis Rodriguez Zapatero immediately announced he will withdraw Spanish troops from Iraq unless the United Nations takes over.
For Italy to do the same would be a severe blow to the U.S.-led war effort -- not so much in troop numbers, but in terms of morale.
The Italian elections are still two years away, but Prodi has doubtless timed his salvo now because of the coming European Parliament elections in June. A poor showing by Prime Minister Silvio Berlusconi's ruling center-right coalition would provide the left with an important springboard into the 2006 parliamentary elections.
As the professor of politics at Rome's American University, James Waltson, puts it: "We are less than three months away from the European Parliament elections, and that will be a key testing ground for the Berlusconi government. And if Berlusconi loses badly -- even though he says he is not going to resign -- it would be a serious blow and could have damaging effects on the solidity of his own coalition."
Both Zapatero and Prodi are using the Iraq occupation as an election issue, knowing that the war is not popular among Spaniards, and Italians. But Waltson points out that neither leader wants simply to "cut and run" from Iraq. They recognize the occupation of Iraq is a reality. What they are seeking is a further internationalization of the situation.
"Neither Prodi nor Zapatero suggests unilateral, unconditional, immediate withdrawal. What they want is to bring the United Nations in, in a bigger way, probably in a controlling way. And this is obviously what the [U.S.] Bush administration is trying to resist," Waltson said.
Spain's shift in position, away from support of the U.S. intervention and closer to the views of France and Germany, has changed the political balance in Europe. The addition of Italy to the same camp would tip the balance further and would mean that four out of the five big EU powers -- with the exception of Britain -- were united in their approach.
Could this influence Washington to relax its hold on the Iraq situation? Alexander Smolar is an analyst with the Warsaw-based Stefan Batory Foundation.
"I think it can influence Washington, possibly in a positive way, in the sense of looking for a bigger presence of international institutions in Iraq. This is a problem of legitimacy -- of whether the United States should act directly as a national entity, or whether there should be a sort of screen, an intermediary, a much stronger presence of international institutions, most of all of course, the United Nations," Smolar said.
There is also concern that the wholehearted support of Poland, a close U.S. ally in the Iraq war, could also start to waver if the antiwar camp makes further gains in Western Europe.
Already, after the Madrid attacks, Polish President Aleksander Kwasniewski made comments which were interpreted as throwing some doubt on Poland's determination. But Smolar does not see Poland's basic position as changing: "There is a very large consensus in the political class, with the exception of some far-right forces, around the important necessity of solidarity with the United States -- even if there are more and more people unhappy with the arguments used to justify intervention, and even if there are more and more people unhappy about the mounting isolation of Poland."
The Polish analyst does, however, see Prodi as having gone too far in identifying and even shaping the political stance of the Italian opposition -- especially since Prodi holds a European office which, by its nature, must be above domestic politics.
"The declaration of Prodi seems to me an excessive case of using his European position to legitimize his domestic political position," Smolar said.
Prodi, a former Italian prime minister, ends his term as European Commission president in November, and will return to Rome to lead the center-left opposition in person. Given his increasing eagerness to take on his old rival Berlusconi, one could say that Prodi's feet may still be in Brussels, but his head is already in Rome.