Like most of the toughest political challenges to Matteo Renzi, Italy's 40-year-old prime minister, opposition to his top choices for the country's next president is likely to spring not from his foes, but from his supposed allies.

Voting for the president of the Italian Republic is usually an arduous ordeal that has produced unpredictable outcomes and dismal failures.

Italy's "grand electors" - just over a thousand lawmakers from both upper and lower houses, as well as regional representatives - begin casting their secret ballots on Thursday to select the country's next president. Given the high two-thirds threshold of the first three rounds, it's a process most observers do not expect to wrap up until early next week.

Quick decision unlikely

For one, there is no clear front-runner to replace the outgoing Giorgio Napolitano, who, at age 89, just cut short his second term. Napolitano had been forced to accept the second term two years earlier when bickering members of the leading Democratic Party failed to agree on a successor. In his acceptance speech, Napolitano gave the lawmakers a thorough dressing down, calling them deaf, inconsistent and reckless. In a striking display of political dysfunction, they cheered.

It's a fiasco Renzi does not want to see repeated, warning Democratic Party parliamentarians yesterday that they "cannot get it wrong" again.

The Democratic Party remains as fractious as it was at the time. DP members currently in parliament were elected before Renzi rose to become party leader and then prime minister. Many of them view Renzi as a politically suspicious upstart who shares more common ground with center-right Forza Italia leader Silvio Berlusconi than with the left-wing roots of their party.

"What's going to make this election interesting to watch," says Daniele De Bernardin, of the political watchdog group Openpolis, "is that on the one side you have a very strong leader, but on the other, you have someone without much power to decide who the new president will be."

No deal with the devil

Renzi's willingness to work with the controversial Silvio Berlusconi, who for Italy's left has come to symbolize what they consider the country's greatest political threats, has only increased his party's misgivings.

Last year, the two men struck a deal known as the "Nazareno pact" in which Berlusconi pledged his support for a new election law, which just passed in the Senate, as well as political and labor reform. This week, after a two-hour, closed-door meeting to hash out possible presidential candidates with Berlusconi yesterday, Renzi emerged reassuring PD senators that he had not made a deal with the devil. Despite Berlusconi pushing hard for the right to squelch any candidate with a history of "leftist activism," Renzi said he would not accept vetoes from the opposition center-right group nor be coerced into accepting its candidate.

The anti-establishment Five Star Movement led by comic-turned-political activist Beppe Grillo refused to meet with Renzi at all, claiming it was clear to them that Renzi and Berlusconi had struck a deal to decide on their own. In an effort to derail the suspected agreement, the Five Star Movement presented 10 candidates its members will vote for on Grillo's blog.

The names consist mainly of older, male politicians from the left, including former Democratic Party leaders Pierluigi Bersani and Romano Prodi. Renzi later met with 10 lawmakers from Grillo's movement who defected, saying they were frustrated with Grillo's authoritarian tendencies and his refusal to work with other parties.

The president's shifting role

Infighting and partisan politics aside, much of the difficulty Italian parliamentarians have had in choosing a new president in recent years is also due to the changing function he has played.

Openpolis' Daniele De Bernardin says, until recently, the president mainly carried out an observational role, meaning he was there to ensure that political parties respected the constitution. However, since the clamorous exit of Silvio Berlusconi as prime minister in late 2011 and the euro zone economic crisis, the political role of the president has grown. As a string of grand coalition governments formed and fell in recent years, it was often Italy's president who provided the country with a form of stability.

While voting for a new president starts Thursday, the crucial round will likely be the fourth one on Saturday. That's when the number of votes needed to elect a new head of state will drop to a simple majority - or 505 of the 1,009 grand electors.

For the first three rounds, where a two-thirds majority must be reached, Renzi has said he may advise supporters to cast blank ballots to forego the hassle of trying to convince smaller parties to back his candidate of choice.

Thus far, that candidate appears to be center-left constitutional judge Sergio Mattarella, a man renowned for his cool demeanor and early opposition to Berlusconi, who could now prove to be an insurmountable obstacle to his election.

But political researcher Daniele De Bernardin says there's an even higher hurdle: "Call it a superstition, but the name people most talk about before the election never becomes the president."