Not since the furore over Coleman Andrews' R232m severance package from SA Airways has the ruling African National Congress (ANC) faced such a testing time.

Clear battle lines have been drawn in the wake of a decision by the Scorpions, led by Bulelani Ngcuka, to ask Deputy President Jacob Zuma a wide-ranging set of questions in a bid to finalise the unit's protracted probe into government's arms deal.

The challenge lies in attempting to work out the coded political speak, to ascertain the extent of the fallout.

Zuma suspects a political motive in the probe, in other words that the race for the next deputy president, and ultimately the president, has begun. This suggests an attempt is being made to clear the way for a new crown prince or princess. Those close to Ngcuka will inevitably fall under the spotlight, the most obvious being his wife, Minerals and Energy Minister Phumzile Mlambo-Ngcuka, and his close friend, businessman Saki Macozoma.

The deputy president may also fear that succession planning is under way in the upper echelons of the ANC now that there is a cloud hanging over him. It makes sense for ANC leaders to consider alternatives, but this makes it no more comfortable for the veteran politician.

Ngcuka in turn has pointed fingers at "criminal comrades" over an anonymous smear campaign. Presumably that relates to the people his unit is now investigating, which include Zuma, his financial adviser Schabir Shaik and former transport minister Mac Maharaj.

The waters are being muddied by the accusations and counter accusations, but one thing is clear for now Zuma's political future hangs in the balance. Even if he is cleared of any wrongdoing, can the deputy president survive to serve another term?

As President Thabo Mbeki said this week, the Scorpions must have good reason to pursue the case. It is the most high profile of investigations the unit has undertaken to date. With so much at stake for Zuma and Ngcuka, it is vital for the unit to be sure of its ground before proceeding.

And the questions being asked of Zuma are telling. Apart from his involvement with Shaik, who is at the centre of arms deal corruption allegations, they range from his knowledge of the credit card licences contract to building a new international airport at Durban.

The implication is that the investigation has moved beyond just the arms deal, suggesting that a wider array of characters may be caught up in the probe.

While Zuma's staying power, and his support within the ANC, should not be underestimated, the second most powerful man in SA is now fighting for his political life. And the ructions will only increase.

The danger for the ruling party is twofold. First, Zuma has been privy to much sensitive information both in his current post and previously as chief of the ANC's intelligence department. Should he feel aggrieved at his treatment, this could be a powerful tool for the deputy president should he be inclined to use it.

Second, unless the furore surrounding the Scorpions investigation is handled with maturity by its leaders, infighting and factionalism could paralyse the party to the detriment of the entire country.

Mbeki has moved to defuse the situation by saying he will not intervene, and that the investigation must run its course. There is an opportunity here for SA's leaders to drive home a commitment to transparency and stamping out corruption. But this particular fight is sure to get uglier before it ends. Cool heads are needed.

Chalmers is editor at large.

With acknowledgements to Robyn Chalmers and Business Day.