Israeli Prime Minister Benjamin Netanyahu is being tested for the authority of his gathering in what is viewed as a trial of his hang on control.
He is confronting long haul rival Gideon Saar in inward Likud party races.
In spite of the fact that Mr Netanyahu is relied upon to win, it comes during an era of mounting challenges for the veteran chief.
He faces preliminary on gift and debasement accusations, just as a third national political race inside a year after two uncertain outcomes.
The BBC’s Barbara Plett Usher in Jerusalem says Mr Netanyahu has battled resolutely, despite the fact that he is generally expected to triumph, since he needs to win huge – else it will resemble his grasp on the gathering is debilitating.
Benjamin Netanyahu: Commando turned PM
Netanyahu: What are the claims?
The leader still has strong help in Likud, yet this is the most genuine inner test he has looked in a time of intensity and shows breaks in the gathering’s assembled front, our journalist says.
There was a snapshot of dramatization at a battle rally in the southern city of Ashkelon on Wednesday night when Mr Netanyahu was guided off stage by protectors after an air assault alarm cautioning of rocket discharge from Gaza sounded.
It was the second time that Mr Netanyahu, who styles himself as the individual who can best carry security to Israel, has been compelled to seek shelter during a crusade rally, following a comparable episode in September.
As surveys opened on Thursday, Mr Saar said that was the ideal opportunity for change.
“I feel an incredible arousing [of voters] in the field. Individuals comprehend that today there is a requirement for a change and God willing together we will roll out this improvement today.”
Mr Saar, who is about 20 years Mr Netanyahu’s lesser, recently filled in as a priest in Mr Netanyahu’s cupboards and is a notable figure in the gathering.