A few short months ago, it appeared to be a done deal. Benjamin Netanyahu was on track to take a fifth term in office at the Israeli general election . A win at the polls would virtually guarantee him the title of Israel’s longest-serving prime minister, snatching it from the country’s founding father, David Ben-Gurion.

But then an army general stepped in. “No Israeli leader is king,” Benny Gantz promised as he kicked off his campaign less than three months before Israelis go to the polls. “I thank prime minister Benjamin Netanyahu for his 10 years of service. We will continue from here.” Gantz, 59, running a centrist party called Blue and White after the Israeli flag, has since climbed rapidly in the polls to become the first serious contender to unseat Netanyahu, 69. The former army chief has no political experience and few concrete policies, but hopes to appeal to voters on one basis more than any other: that he is not Netanyahu.

Last week, as Israel’s attorney general said he intended to indict Netanyahu in three separate corruption cases, that decision appeared prescient. The prime minister, who denies wrongdoing, claimed that the legal case against him was a political ploy “just to topple the right wing and raise the left to the premiership”. Gantz replied just half an hour later: “Israel deserves better.”

Tall, blue-eyed and silver-haired, Gantz has the look of a political star, but his lack of political heft and fondness for opaque promises has provided fodder for critics. But if Israel’s history shows a theme in politics, it is that voters hanker for a leader with military credentials. Gantz is the 12th chief of staff to enter politics. Two of his predecessors, Yitzhak Rabin and Ehud Barak, became prime minister.

“Chief of staff is probably one of the most important, if not the most important, public positions,” said Yohanan Plesner, a former politician and president of the Israel Democracy Institute. His thinktank found that 78% of the public trust the Israel Defence Forces, while only 30% trust the government to the same extent. “[Gantz] has been in politics for a few months, but he has been around for decades. Chiefs of staff are not newcomers to the Israeli public scene,” he said.

Gantz has sought to appeal to both sides of a country where political divisions run deep. His message is one that many are eager to believe: “There is no more right and left, there is only Israel before everything,” goes his party’s jingle. But many of his policies remain a mystery, to the extent that the Haaretz newspaper called his older sister to inquire what they were. Even she, it found, “didn’t know his political views”. Gantz’s team have denied requests for an interview.

To appease as many people as he can, Gantz has had to appear simultaneously rightwing and leftwing. On security issues, he has pushed the message of being both a dove and a hawk. Head of the army from 2011 to 2015, his campaign released a short clip showing a bomb-flattened neighbourhood in Gaza after the 2014 war he led. “Only the strong wins,” reads text on the video, which boasted that Israel killed more than 1,364 “terrorists”. (The claim contradicts a United Nations inquiry that found more than 2,200 Palestinians were killed, more than half of them civilians.) Yet Gantz said in another video that there is “no shame in yearning for peace” and has promised to strive towards a deal with the Palestinians.

The mixed messaging has worked, according to analysis by Alon Yakter, a lecturer at the school of political science at Tel Aviv University, and Mark Tessler at the University of Michigan. Gantz’s “success is because of, not despite, his vagueness,” they wrote in the Washington Post. He appeals to what they call a large number of “sceptical doves” – voters who support a peace deal in theory, but doubt it is possible.

Ultimately, Gantz is betting on Netanyahu fatigue. For years many Israelis have been dissatisfied with the leadership of the man they know as Bibi, but have not backed a candidate to replace him. Gantz has focused on how Netanyahu has sowed division and battered state institutions such as the police and judiciary to stay at the top of government.

But the veteran also faces battles to uphold his virtuous image. Gantz is being sued by a family in Gaza in a Dutch court for war crimes and was accused last week of sexual misconduct as a senior in high school. It is unclear how those allegations, which he denies, will sway voters. On the campaign trail, Gantz has made sure attention is focused on Netanyahu and his vices. “Your time is up,” he said. “We are moving onwards.”