Many months have passed since the Knesset has performed its primary duty – legislating on behalf of the public good. Instead, it has been fixated on itself. By means of the Central Elections Committee, some Knesset members are focused on the question of whether specific individuals and lists will be allowed to run in the next election. Sitting as the Knesset House Committee, and then in the plenum, they must decide whether one of their colleagues will be granted immunity from criminal prosecution.These two issues that are preoccupying MKs currently, share one thing in common: in both cases, Knesset members are performing a quasi-judicial function and serving as both judge and jury. They must interpret Section 7A of the Basic Law: The Knesset, whose heading is “Barring Participation in Elections,” and Section 4 of the Knesset Members (Immunities, Rights, and Duties) Law, “Immunity from Prosecution,” and then apply them in the actual cases before them. In this quasi-judicial role, our elected representatives are called upon to exercise their own discretion. They are not bound by their party’s position or by coalition or opposition discipline. Furthermore, in total contrast with the Knesset’s usual routine, they must not promote any political agenda or represent a specific sector of the population. Like judges, they are required to exercise their authority for the common good. They must be motivated by true non-partisanship rather than by sectoral interests, when they decide whether to deny some citizens the basic right to elect and be elected, and whether to violate the principle of equality before the law by granting immunity to a favored few.But alas, the way in which the Knesset has exercised these powers in two recent cases is disappointing, to put it mildly. The proceedings and their outcomes have demonstrated that political affiliation is the decisive factor: tell me what party you belong to, and I’ll know whom you will bar from running for the Knesset and to whom you will be willing to grant immunity. One end of the political spectrum disqualifies the other end, even though, in this quasi-judicial process, ideology is not supposed to be a factor in how MKs vote. But in the case of a MK against whom the attorney-general has decided to file an indictment, the members of his party and of his Knesset bloc vote as one – to grant him immunity rendering apparently his political identification as the sole criterion for their decision.When the outcome is known a priori and MKs’ positions are determined from the outset by irrelevant considerations, it is hard to attribute great importance to the proceedings. In fact, the harm they do – in undermining public trust and fostering contempt for the Knesset – is inestimable; while the benefit is negligible, since the final word rests anyhow with the Supreme Court, which must rule on whether the Knesset’s decisions are reasonable.Today, it is a common practice to bash the court for its use of the test of reasonableness when reviewing actions by the other branches of government. But the way Knesset members are exercising their power – by pre-programmed conduct on issues that require their autonomous discretion – makes it quite clear, to anyone with common sense, that we need the court to review the reasonableness of their decisions. Otherwise, the members of the outgoing Knesset will have the power to make the final decision about who can run against them in the next election. Without judicial review they will be able to protect one another through the mechanism of parliamentary immunity. We need a responsible adult – the court – to clear away the political background noise and exercise objective discretion in order to reach a decision.When Knesset members mix “political” and the “judicial” functions it teaches us something about the candor and quality of their arguments against the judicial system. One might have expected that those who are most strident in their criticism of the Supreme Court for having an “agenda,” would provide us with an example of how semi-judicial authority should be exercised properly. But no – the pot has been calling the kettle black!And were that not enough, some of our legislators want to revise the means for the selection of judges and entrust that power (directly or indirectly) with the Knesset. Such a change would destroy the boundaries that currently separate between the branches of government, and the Israeli courts would become openly biased – politically and ideologically. To ward off this danger, we need to hone the functional and institutional distinctions between those whose business is politics and those whose profession is justice.The writer is a senior fellow at the Israel Democracy Institute and a professor of law at Bar-Ilan University.