Italy’s center-left Democrats are expected to win the most votes in parliamentary elections this weekend, but they could struggle to win a majority in the upper chamber, where centrists backing incumbent prime minster Mario Monti may end up holding the balance.

Berlusconi’s change of heart

Monti, a former European commissioner who assumed the prime ministership in late 2011 when Italy seemed to teeter on the brink of sovereign bankruptcy, resigned in December when his predecessor, Silvio Berlusconi, pulled his support.

The conservative cited a collapse in home sales as a result of a new property tax, economic stagnation and tepid labor market reforms as reasons for withdrawing from the government.

Berlusconi has since campaigned against Monti’s economic reforms, promising to scrap the property tax and take no orders from Germany, which he claims dictates the incumbent’s austerity program.

Anti-German rhetoric

Germany insists on fiscal consolidation and economic liberalization in the south of Europe, where countries have seen their debts and borrowing costs rise in recent years, jeopardizing the stability of the single currency.

The anti-German rhetoric appears to resonate with voters. Whereas the left-wing Democratic Party, which also backed Monti’s reforms, enjoyed a 15-point lead in polls as recently as early January, the latest surveys put Berlusconi’s party and the federalist Northern League behind by just 5 percentage points.

Bonus seats

Democratic Party leader Pier Luigi Bersani has only to squeeze out a minor victory for the left in order to gain a majority of the seats in the lower house of parliament, where the biggest party automatically gets the most seats.

But in the Senate, winners’ bonus seats are awarded on a regional basis and the two camps are close to a draw in battleground regions, including Lombardy and Veneto, which between them elect 73 senators. (Hence Berlusconi’s alliance with the Northern League.)

Alliances

Bersani still has the best chance of becoming prime minister, but he might need to sacrifice his alliance with the far-left Sinistra Ecologia Libertà in order to lure centrists to his side.

Sinistra Ecologia Libertà did not support Monti’s reforms. Party leader Nichi Vendola has dismissed the possibility of joining a coalition that includes the incumbent prime minister’s supporters as “fantasy politics.”

Monti, for his part, has all but ruled out a coalition with the right as long as it is led by Berlusconi. He told Italian radio last month that he had “no intention of making any agreement with parties that aren’t strongly reformist,” but he also said he could “easily imagine a collaboration” with the right if Berlusconi stepped down.