The Prodi government’s several headaches stemmed from its slender majority in the Senate, where, according to the 2005 electoral system, regional premia make it harder for a nationwide coalition to build a strong majority. In 2006, the left lost out: as its commanding national leader withered in the heat of the campaign, it lost a strong Senate majority. Could the same happen in reverse in 2008?

The graph below shows the possible scenarios for the distribution of seats with different shares of the vote. The assumptions are as follows:

1. The centre-left will be divided between the Partito Democratico + hangers-on, and the Sinistra Arcobaleno;
2. These two will split their support in roughly the current ratio the polls suggest (9:33), and this split stays the same at all levels of combined left support;
3. The swing to/from the left will be uniform and national…
4. … and one can calculate a swing from 2006, when the left ran united, to 2008, with a different set of coalitions;
5. The seats abroad, and in Trentino Alto-Adige and Val d’Aosta, will remain as they are

From 40% to 44%, the left is runner up everywhere, as its internal divisions cost it even in its heartlands. The combined left is currently polling in this area.

From 44% to 50%, the left cuts into the centre-right’s majority. At the top end of this range, the left wins 154 seats (155 including Luigi Pallaro from South America, if he were to be returned again) with the centre-right on 161. This would leave the centre-right with a majority of all the regularly elected Senators; it would still, however, have to rely on at least one senator for life.

Only once it reaches a combined share of 51% of the vote does the centre-left regain the same, narrow majority it had before the dissolution of the two Chambers.

Thus, the centre-left would have to poll 8 percentage points better than it’s doing now to make a pareggio in the Senate a realistic possibility. Is that realistic? Hardly. Even the centre-right’s incredible come-back in 2006 only bought it five points compared to its early December 2005 low. Veltroni may (just!) be liked more than Berlusconi, but he would have to do some heavy lifting to endanger the centre-right’s current lead.