Israeli Prime Minister Benjamin Netanyahu unleashed a harsh verbal attack Sunday against his potential replacement, rightist rival Naftali Bennett, declaring it would constitute the “greatest election fraud” in Israel’s history if his own reign as the country’s longest-serving leader were ended.

With a parliamentary vote of confidence in a prospective new Israeli government to take place as early as Wednesday, Bennett, 49, retorted that it was time for the 71-year-old prime minister, his onetime mentor, to “let go and allow Israel to move forward.”

In the wake of four inconclusive national elections, political passions are running high in advance of the showdown between Netanyahu and a diverse coalition arrayed against him, which is drawn from Israel’s political left, right and center.

Israel’s domestic security agency, the Shin Bet, issued an unusual warning over the weekend that rising political incitement could lead to violence, and security has been tightened for several members of the “change coalition” seeking to unseat Netanyahu, who is being tried on corruption charges.

In an address to members of his conservative Likud party on Sunday, Netanyahu lambasted Bennett over earlier pledges that he would not join forces with centrist politician Yair Lapid, the coalition’s leader, or with other participants in the new political grouping seeking to oust him.

Denouncing that alliance, Netanyahu told party allies, “We are witnesses to the greatest election fraud in the history of the country and, in my opinion, the history of democracies.”