Paolo Gentiloni, the new prime minister of Italy, has won a vote of confidence in Italy’s senate, in a move that will allow his government to formally take office amid relentless political attacks. The 62-year-old former foreign minister was backed by the upper house of the Italian parliament on Wednesday in a 169-99 vote. But, ever since he was chosen to take on the role of prime minister on Sunday, Gentiloni has faced criticism from opponents determined to ensure that he does not enjoy a political honeymoon.

He was appointed by Sergio Mattarella, Italy’s head of state, following the resignation of Matteo Renzi, the centre-left prime minister who suffered a humiliating defeat in a high-stakes constitutional referendum earlier this month. Now facing a tough populist and rightwing backlash, the new prime minister – who comes from an ancient Italian noble family – has had a shaky start.

Although Renzi, who is still the head of the Democratic party (PD), has resigned from office, his shadow looms large over the prime minister’s residence at Palazzo Chigi. For now, Renzi is still considered the favourite to represent the PD if and when early elections are called in 2017.

Gentiloni’s decision to keep almost all of Renzi’s key cabinet members and political allies in the government, including Maria Elena Boschi, the author of the failed constitutional reform, has prompted accusations by opponents in the Five Star Movement (M5S) that the government is still being controlled by Renzi and that it is illegitimate given the former prime minister’s resounding defeat.

Luigi di Maio, who could represent M5S in early elections, compared the situation unfavourably to Brexit, saying that at least when David Cameron resigned following his defeat he was not heard from again.

Beppe Grillo, the comedian and founder of the anti-establishment M5S, arrived in Rome on Wednesday to meet other party leaders to discuss their opposition strategy, including plans to stage protests against the Gentiloni government across Italy.

Gentiloni’s tenure is expected to be relatively short. His most important task will be to oversee a change in Italy’s electoral law, which will have to be passed before the next election can be called. He could also be forced to oversee a multi-billion-euro rescue of Italy’s third largest bank, Monte dei Paschi of Siena, in the event that the bank does not secure enough investors for a private recapitalisation. A rescue could happen as soon as Friday.

While Gentiloni told lawmakers this week he was keen to build on Renzi’s agenda, focused on economic issues, the danger for the Democratic party is that it is being labelled as increasingly out of touch with Italian voters.

“Renzi made a giant mistake saying he would resign if he failed the referendum, and now being perceived as the puppetmaster. Italians don’t care if he is the prime minister or not, but they care if he is the puppetmaster,” said Giovanni Orsina, a professor of Italian politics at LUISS University in Rome.

“It looks like a gigantic lie. And the fact that the composition of the government is so similar – it is still Renzi’s government in disguise. What they should try to do now is try to regain votes from the Five Star Movement, and this government, instead, is giving more votes to the Five Star Movement,” he added.

In light of growing fears in the US and Europe about the role of fake news in politics, Italian newspapers were also quick to point out that an alleged satirical news website was the source of a false political attack on the new prime minister that went viral. The website, called Libero Giornale, falsely – or satirically – quoted Gentiloni as saying that Italians had to start making “small sacrifices” and “stop whining on social media” if they wanted to become competitive. The article was shared over 10,000 times in only a few hours, according to a report in La Repubblica.