Israel’s two main parties are dragging each other down into the mud as the election enters its final straight before voters go back to the polls on Monday — an unprecedented third election within 12 months.

Likud initially planned to run a “positive” campaign focusing on Prime Minister Benjamin Netanyahu’s achievements in what they describe as “the best decade in Israel’s history”.

But it has instead launched a smear campaign against its main rival, Blue & White leader Benny Gantz.

• Interactive guide: the parties running in this election

“Something not good is happening to Benny Gantz,” Mr Netanyahu said in a rally on Tuesday night. “And this raises questions whether we can take a risk with our future.”

He did not go in to detail but he was alluding to rumours spread on social media by Likud outriders speculating about Mr Gantz’s mental health, as well as lurid details of sex videos allegedly found on his phone when it was reportedly hacked by Iranians.

This week it was also reported that Mr Netanyahu’s lawyer had hired a private investigations company to dig up embarrassing details on Mr Gantz, although the lawyer denied this.

In response, Blue & White, which earlier in the campaign were reluctant to focus too heavily on the indictments on Mr Netanyahu, openly accused him of further corruption in the “submarines case”.

Gabi Ashkenazi, number four on Blue & White’s list and its candidate for defence minister, accused Mr Netanyahu of having lied to defence chiefs about the acquisition of submarines and promised to form a commission of inquiry into the matter after the election.

Mr Netanyahu has already been cleared by the attorney general of any criminal involvement in the submarines affair.

Both parties’ desperation is due to the polls, which project yet another stalemate emerging. So far the polls have barely budged from the previous election’s results.

In recent days, they have detected a small move towards Likud, which is now predicted to win more seats than Blue & White, but this gain has largely been at the expense of Likud’s coalition allies and the deadlock between the two main blocs remains.

None of the polls conducted in the past month show Mr Netanyahu’s coalition of four parties — Likud, along with Shas, United Torah Judaism and Yamina — with a majority.

The best result so far for them has them on a total of 58 seats, still three away from a majority.

But while there is likely to be a majority in the next Knesset for parties opposed to Mr Netanyahu, Mr Gantz does not seem to have a enough for a coalition either.

Blue & White and Yisrael Beitenu both refuse to be part of any coalition backed by the Arab-supported Joint List, let alone allowing them to be partners in government.

Without the Joint List, Mr Gantz is  even further from a majority than Likud’s bloc.

Another option would be to form a minority government along with Yisrael Beitenu and Labour-Gesher Meretz, with the Joint List abstaining, but that also seems a distant prospect.

As bizarre as it sounds, there is already talk in Israel of a fourth election and the Central Election Commission has even begun early preparations for such an outcome. September 6 is seen as a possible date.

Unless Monday’s result is drastically different from the polls, the only way of avoiding yet another election would be a national unity government in which Likud and Blue & White are the main partners and the two leaders somehow find a way to split the prime minister’s term between them.

But for this to happen, either Mr Gantz has to give up his veto on serving under a prime minister who has been indicted for criminal charges, or the unthinkable has to happen and Mr Netanyahu agree to someone replacing him, at least for the time being.