Israel’s longest-serving prime minister is poised to face one of his most dangerous political challenges in a decade on Thursday when the ruling Likud party holds a leadership primary to decide who will lead it in the next election.

The internal vote arrives at a particularly fraught time for Benjamin Netanyahu, wounded by three damning corruption indictments as well as growing internal dissent over his failure to score decisive wins in two inconclusive national elections.

Most alarming for the 70-year-old leader is a public challenge from a Likud party favourite, Gideon Saar, who broke ranks this month to launch a leadership bid. While his chances of replacing the party’s most successful ever leader are still seen as low, the veteran politician’s short campaign has gathered rapid momentum.

Calling for a “renaissance” of the Israeli right, Saar has focused on Netanyahu’s inability to form a government, a failure that has tipped the country into months of political paralysis. An unprecedented third national election is set for 2 March.

“He (Netanyahu) has failed twice, but it is not because of the Likud’s ideas,” Saar said as he launched his campaign. “If we do not make a change, we are getting close to a leftwing government,” he warned as supporters chanted: “Only Saar can!”

Despite his outwardly restrained manner, the former interior and education minister has often been pegged as the next Likud leader. His is talked about excitedly in rightwing circles by those who see him as quietly capable.

In an apparent attempt to woo Netanyahu fans – but ones who are hankering for change – Saar promised on Monday to push to get the prime minister appointed as Israel’s next president.

The 52-year-old former lawyer and journalist was brought into politics by Netanyahu two decades ago. But he left in 2014 for five years after tensions rose between him and the prime minister, who saw him as a threat. Last year Netanyahu accused Saar of orchestrating a coup against him.

In October, after another muddied election and as Netanyahu’s legal woes began to snowball, Saar openly challenged him – a rarity in a party known for fierce loyalty – with a single tweet. When Netanyahu suggested he would consider a leadership battle to firm up his mandate, Saar responded on Twitter: “I’m ready.”

A staunch nationalist, Saar is seen as even more hardline regarding Israel’s continuing control of the Palestinian territories, but within Israel’s domestic politics, he is considered pragmatic.

Vitally, many think Saar could forge a deal with the opposition Blue and White party if the March election delivers a similarly uncertain result, as polls have predicted. Blue and White’s leader, the former army chief Benny Gantz, has ruled out joining a coalition with a prime minister under indictment but not other Likud figures.

Netanyahu and Saar have toured the country this week to rally support. Israeli media predict a solid win for Netanyahu, although Saar has gained backing from a handful of Likud lawmakers and hundreds of activists.

The stakes could not be higher for Netanyahu, both professionally and personally. Charges against him include fraud, breach of trust and bribery, which could lead to jail time. If he retains the role of prime minister, Netanyahu is not legally obliged to step down from public office and could use his position to push for immunity.

Netanyahu has denied all allegations as a “witch-hunt”.