Deputy President Jacob Zuma seems to have a rather short memory. If he had paid any attention to the content of the oath he was constitutionally required to take when he was sworn in as deputy president in 1999, he has apparently now forgotten that he had promised the nation to obey, observe, uphold and maintain the constitution and all other laws of the republic.

How else can one explain his recent decision to lay a complaint against the national director of public prosecutions, Bulelani Ngcuka, with the public protector?

From a constitutional law perspective, it is deeply troubling that a high-ranking member of the executive seems intent on undermining the independence and credibility of the constitutionally created office of the national director of public prosecutions.

Equally troubling is the fact that Public Protector Lawrence Mushwana, seems willing to endorse this disregard for the constitution and the ordinary laws of the republic, and to entertain a complaint that cannot but undermine our hard fought-for constitutional democracy.

Zuma and his supporters will argue that he has a right to clear his name and that he is making a legitimate case in the public interest against the abuse of power by a public figure.

But Ngcuka is not an ordinary public figure. As national director of public prosecutions, he is in charge of the criminal prosecution policy of the country, a position explicitly created by the constitution. The constitution also states that legislation must ensure that the prosecuting authority exercises its functions without fear, favour or prejudice.

The legislation ensures this by prohibiting any organ of state or any official from improperly interfering with, hindering or obstructing the prosecuting authority in carrying out its duties. Legislation also indemnifies anyone in the office of the prosecuting authority against liability for anything done in good faith in the course of their duties.

There are excellent reasons why the law protects the prosecuting authority against interference from the powerful and the corrupt. It is of utmost importance for the administration of justice that the criminal justice system must not be seen to be open to manipulation and abuse by people with influence or political connections.

Were the public to lose confidence in the impartiality and legitimacy of the prosecuting authority, it will begin to erode respect for the law and will potentially lead to an erosion of the rule of law itself.

It is also important that the prosecuting authority is not exposed to continuous attacks by opportunistic individuals with power and money who happen to find themselves on the wrong side of an investigation or under threat of prosecution.

Imagine the chaos which would result if the prosecuting authority were forced to respond to allegations levelled against it by every second Mpumalanga official caught with his or her hands in the till.

Worse, still, imagine the effect on the administration of justice if the public protector decides to vigorously investigate these claims, to clear up public confusion in each and every case.

The prosecuting authority would be unable to do its constitutionally mandated job and the criminal justice system would collapse under the strain.

Zuma and his supporters will probably respond that the director of public prosecutions is not above the law, and that if he has abused his power, it is in the public interest to expose this abuse.

This is, of course, correct. We live in a constitutional democracy and nobody - not the national director of public prosecutions or the deputy president - is above the law. But because of the special position of the prosecuting authority in the administration of justice, the constitution and the relevant legislation provides for special ways to deal with this problem.

The constitution recognises that the prosecuting authority cannot do its work in isolation, and therefore ensures that the authority is accountable to both the minister of justice and to parliament.

The minister of justice has final responsibility over the prosecuting authority, and if one of his colleagues believes that the national director of public prosecutions is abusing his power, he is obliged to raise it first with the minister.

In the present case, it is clear that Penuell Maduna, the minister concerned, has backed Ngcuka and does not share Zuma's negative view of him. It is therefore extremely peculiar that Zuma has nevertheless laid a complaint against Ngcuka with the public protector.

It displays a spectacular lack of respect for the constitutional architecture put in place to safeguard the impartiality and independence of the prosecuting authority and places a question mark over Zuma's respect for the constitution.

By going over the head of a cabinet colleague he is also, in effect, suggesting that the minister is not doing his job properly. In most democracies the president would have been forced to rein in or fire either the minister of justice or the deputy president, but President Thabo Mbeki has retained his sphinx-like silence on the matter, suggesting that he is powerless to stop the squabbling among members of his cabinet.

Moreover, the prosecuting authority is also accountable to parliament, and the national director can be summonsed by any parliamentary committee to explain and defend his actions. One would think that a deputy president, steeped in the values of democracy and mindful of his duty to uphold and maintain the constitution, would use the parliamentary avenue to deal with his complaints against the national director in a responsible and a constitutionally sound manner.

Yet he has chosen to bypass parliament and to go straight to the public protector, thereby guaranteeing maximum publicity for his case while further undermining the credibility and independence of the national director. The decision of the public protector to entertain the complaint from the deputy president is also highly troubling.

First, the public protector has the power not to investigate a complaint if the complainant had not exhausted all other legal remedies - something Zuma has not done. Second, he has decided to investigate a complaint of abuse of power against another independent constitutional agency on the basis of the flimsiest evidence.

The fact that the constitution explicitly prohibits the public protector from investigating court decisions suggests that the drafters of the constitution were aware of how dangerous it would be to have the public protector involved in matters relating to the administration of justice.

Although the constitution does not explicitly prohibit the public protector from investigating abuse of power by the prosecuting authority, the dangers of undermining the independence and impartiality of the prosecuting authority through the entertainment of frivolous claims is so great that this power should only be used in the most extreme cases.

Thus, if Zuma could present hard evidence of Ngcuka being involved in a conspiracy against him - something that he has singularly failed to do, so far - the public protector might be justified in investigating the matter because it would provide evidence that Ngcuka is not acting in good faith. In all other cases, his decision to entertain the complaint is at best unwise and at worse amounts to an abuse of his power.

Zuma's recent actions therefore undermine our constitutional democracy. Certainly, it has undermined the credibility of Mushwana, whose pronouncements will soon be just as believable as those oft-repeated claims by Donald Rumsfeld that all is going hunky-dory in Iraq.

And even if Zuma is cleared of all corruption charges, his recent actions place a question mark over his suitability to hold any high public office in South Africa.

Professor De Vos is based at the Department of Academic Teaching and Development at the University of Western Cape.

With acknowledgements to Pierre de Vos and the Cape Times.