Two months ago, Italy’s main centre-left party, the Democratic Party, elected a new leader: Matteo Renzi, the young (then 38) mayor of Florence, who has a strong reputation as a centrist and a moderniser. He is said to regard former British prime minister Tony Blair as a role model.

The odd thing about this was that although his party was in government, Renzi did not thereby become prime minister. Enrico Letta remained in the top job, at the head of an unwieldy grand coalition formed after last year’s indecisive election. This was never likely to work as a long-term arrangement.

Now, sooner rather than later, Renzi has made his move. Yesterday, the Democratic Party’s leadership committee voted to support a change of government. Letta, having earlier resisted the idea, conceded defeat, announcing that he would present his resignation today to Italian President Giorgio Napolitano.

As Le Monde‘s correspondent Philippe Ridet put it, it was “concise, surgical and even cruel”.

No one regards Letta’s government as having been much of a success. Although there are modest signs of improvement, Italy’s economy remains in dire condition. The The Guardian reports “more than 41% of young people out of work, and a public debt of more than €2 trillion”. If a lack of dynamism at the top was the problem, then Renzi — whom Ridet refers to as a “high-speed train” — can be expected to make quite a difference.

But the problem is that the change is only likely to happen at the top. Renzi will still depend on the same ramshackle coalition as Letta did: not so much in the lower house, where the Democratic Party has a majority in its own right (courtesy of the electoral system), but in the powerful Senate, where it depends on a collection of centrists, local autonomists and a breakaway centre-right party.

Angelino Alfano, leader of the New Centre-Right party, has already served notice that his support cannot be taken for granted — he wants an assurance that Renzi won’t try to hang on for the full term of Parliament, until 2018 (an unlikely prospect), and warns against the government moving to the Left.

On the other hand, being too far to the Left has certainly not been thought to be Renzi’s problem — quite the opposite. In a party still deeply divided between ex-communists and ex-Christian-Democrats, he (like Letta) represents the moderate wing; his major difficulty is probably going to be getting any serious economic reform program past his party’s leftists.

Moreover, it’s not just economic reform that Italy needs. There’s general agreement on a need to do something about the recurring political deadlock, but electoral reform remains a very large can of worms. Opportunities in politics have to be seized when they arise, and Renzi is clearly an ambitious man, but even he must have doubts about the magnitude of the task he’s taken on.

Full marks at this point to the BBC, which managed to produce a whole report on the changeover without mentioning the name of Silvio Berlusconi. Unfortunately, “Il Cavaliere” cannot be dismissed quite so easily. Although out of Parliament, he remains leader of the largest centre-right group, Forza Italia, and his in-principle agreement last month with Renzi on electoral reform was a major step in sidelining Letta.

Forza Italia is still in opposition, but ideologically it is probably closer to the Democratic Party than Alfano’s group. That might give Renzi some additional options, but also some additional headaches: nothing is likely to alienate his own Left wing more than an accord with Berlusconi.

Italy’s distinctive political history — long years as effectively a one-party state, followed by dramatic fragmentation of the party system in the 1990s — continues to cast a long shadow. It’s now in a chicken-and-egg situation: electoral reform may (or may not) produce greater stability, but a measure of stability is necessary to get it (or any other reform) approved in the first place.

Matteo Renzi might be the man to break out of this circle, but he will need a lot of luck.