With the piling up of criminal affairs, linked to Prime Minister Netanyahu and his family, the question is whether the Shin-Bet is charged only with securing senior politicians, or also securing the nation against its senior politicians... In the US similar questions were answered already in the 1950s, in Eisenhower's Farewell Address...
The list of criminal affairs associated by Israeli media with Prime Minister Netanyahu and his immediate family is steadily growing. Some of the latest involve suspected massive voting fraud,  unlawful receipt of substantial funds, detailed in a French court by "Sting of the Century" convict Arnaud Mimran,  and unlawful receipt of substantial funds, funneled through a close family member (rumored to be his unemployed son), from US donors, some of whom are also the target of criminal investigations in the US. 
Opinion piece by Amir Oren in Haaretz (Hebrew only, missing in the English edition) today is titled: "What is the Shin-Bet afraid of". 
Oren is a reputable Israeli security analyst, who also worked for CBS during the 2003 Gulf War and the 2006 Israeli invasions of Lebanon, published in the New Republic and The Economist, and was affiliated with the The Washington Institute for Near East Policy.
Oren raises the question, whether the Shin-Bet would, should, could cooperate in investigations against Netanyahu and his family members, in case the personal security detail were witnesses to some of the suspected criminal conduct, now under "examination". (According to new routines of the justice system, "investigation" is initiated against normal citizens following credible criminal suspicions. Under similar circumstances, pertaining to senior political figures, only an informal "examination", which is not defined by law, is initiated.)
Oren's opinion is that the Shin Bet is charged with protecting the Prime Minister, but also with protecting the public against criminality by the Prime Minister and his family...
The opinion piece concludes:
The most dangerous risk is internal, including the security detail itself, as seen in numerous assassinations worldwide. The Shin-Bet requires periodic polygraph tests for high security clearance individuals. The Attorney General should order that the security detail also be asked whether they were witnesses to criminal conduct by the personality, whom they secure, and his family members. It is the national duty of the Shin-Bet to abandon its passive acquiescing partnership in such criminality. Lying in such polygraph tests should lead to relieving security personnel of their duties. The truth should assist police investigations and State Prosecution discussions regarding the Netanyahu files. Securing the State against its senior leaders, if they sinned, is of no lesser importance than securing the person himself.
It is doubted that such opinion is shared by the Shin-Bet... It is also often doubted that the Israeli justice system today can deal with such matters: The Attorney General, Police Chief and Shin-Bet Head are personal appointments by Netanyahu. Some of them were opined dubious appointments, specifically regarding conflicts between interests of the office and Netanyahu's interests.
The Israeli regime was hijacked by a Shin-Bet-judiciary gang.  The Shin-Bet and the judiciary two are central power groups, whose loyalty, the evidence shows, is only to themselves..
In the US similar questions were answered already in the 1950s, in Eisenhower's Farewell Address, and Hillary Clinton's email scandal was only the latest episode of this kind.
 Zernik, J. "ISRAEL: Computer fraud in the Central Election Commission? Where is the Shin-Bet?"_OpEdNews.com
 Alfon, D. "Benjamin Netanyahu's Shady French Connection"_Haaretz