Italy referendum: Matteo Renzi bets on Obama's blessing

Barack Obama has offered his support to Matteo Renzi ahead of the referendum

There are three rules when it comes to getting involved in other countries' civil wars, and they apply to elections too.

First rule: don't get involved. Second rule: if you must get involved, pick a side. Third rule: make sure your side wins.

US President Barack Obama ran foul of the rules when he supported David Cameron in the UK's EU Referendum in June. Mr Cameron lost.

The president is now taking his second bet of the year on a European ally. Italian Prime Minister Matteo Renzi has called a constitutional referendum on 4 December.

"As you fight for this cause of reform, know that we stand with you," said Mr Obama during the Italian leader's visit to the White House on Tuesday.

Mr Renzi said: "If we win the December referendum it will be easier for Italy to carry on the battle to change the EU."

The two men's affection for one another was clear. Each is a centre-left politician, facing opposition from rising populist movements.

But the prime minister's opponents in Italy concluded that the president's support was a jinx.

Politicians criticise Renzi meeting on social media

Right-wing leader Giorgia Meloni tweeted: "Tonight two presidents about to expire had dinner together at the White House. One expires on November 8th, the other one on 4 December"

"Someone should tell [Mr Obama] that the endorsement of the American president brings bad luck. Brexit should have been a lesson," wrote Renato Brunetta, a Forza Italia lawmaker campaigning for a No vote

Katya Adler: Renzi's Brexit blues and risky referendum

Italy's constitutional conundrum

Beppe Grillo, leader of the populist opposition Five Star Movement, said: "Our country is dying and those responsible for governing go to the other side of the world to film a pro-Yes spot for the referendum.

"Every day that passes without the Five Star Movement in power is one more day of agony for Italians."

President Obama's decision to back David Cameron's Yes campaign before the UK's EU referendum ultimately failed

Italy's referendum is about power and who gets to wield it. Mr Renzi wants more of it for the elected government, as a way of reforming a political system he considers to be outdated and overcomplicated.

Mr Renzi proposes two specific changes: to simplify law-making by stripping Italy's upper house, the Senate, of most of its powers; and to give the elected government in Rome decision-making powers currently held by regions. He's threatened to resign if he loses (a threat that he's slowly begun to retract).

His opponents say the referendum is a simple power-grab. Prominent Italian politicians, including the two most recent prime ministers, Mario Monti and Silvio Berlusconi, have announced their decision to vote No.

Now Mr Obama has weighed in with his endorsement.

"How do you interpret the [Obama] endorsement?" wrote Paolo Pombeni, a journalist for Italy's Il Sole 24 Ore newspaper.

"It is the symbol of an American judgement of Italy's fragility. The US government thinks that political stability - and hence also economic and social cohesion - is at risk."

Current opinion polls show a race that is too close to call. Every vote will count. Well, apart from any cast from 1600 Pennsylvania Avenue.