It was time for Helen Zille to go. Now the question that looms large over the DA is this: What now and led by whom? How to move from the 22% that it achieved in last May's elections to a higher take of the electoral haul? For now, however, we will be obsessed with diagnosis of the reign of Zille. Over the past two years the DA leader has made some serious strategic and tactical mistakes (remember the disastrous Agang SA non-merger?). She became shrill and irritable with party members and the media, and was losing focus on the important issues facing her party, her supporters and South Africa.Make no mistake, Zille has done an incredible job as leader of the party over the past eight years. Electorally the party has grown by leaps and bounds - but has failed to reach the 30% of the vote it aimed for in the last election.She inherited a party perceived as rabidly right-wing in 2007 and softened it. She lauded and supported the National Development Plan, thereby subtly pushing the party into more centrist politics and away from the hardcore capitalism of the 1990s DA. Crucially, though, since 2007 she has exposed the corruption and bankruptcy at the heart of our current political leadership.Her rise to the top coincided with the rise of President Jacob Zuma, and he will be heaving a massive sigh of relief as she rides into the sunset.Zille has run him ragged, exposed his attacks on the constitution and called him out on his laissez faire attitude towards public money.Under her leadership, the DA has begun to counter the narrative that the DA is a "white" party. Patricia de Lille, Lindiwe Mazibuko, Mmusi Maimane and others have emerged as leaders.The DA's showing in last year's elections was helped by the fact that there is a new cadre of black supporters emerging. The party that was exclusively the domain of the Democratic Party-National Party marriage of the late 1990s was, under her, changing, and fast.But the growth of that diversity has been both a boon and a challenge because the DA was perceived as just "not black enough" and not changing fast enough."Diversity matters in South Africa," Zille said yesterday.This means that the pressure is on for a black leader of the party. That pressure will take centre stage over the next four weeks. Zille will not be excluded from this debate. Despite her protestations to the contrary, many will ask whether the timing of her departure was not made in such a way that it limits the field of new leaders who can fill her shoes.Zille will have to watch the effect on the party of her decision to step down.In her powerful position as premier of Western Cape she will have to force herself to allow the new leadership to run the party and not interfere.The party is theirs to steer now. She has done her bit and any attempt to interfere would backfire spectacularly.A challenge lies ahead for the DA in opposition politics. Zille criticised Zuma incessantly for seven years. Then along came Julius Malema and the Economic Freedom Fighters.The upstart party has set the agenda in parliament, eclipsing the DA in a forum in which the likes of Tony Leon and Lindiwe Mazibuko used to haul the ANC over the coals. In today's fluid politics, in which the sound byte can sometimes be more powerful than sound policy, this presents a major electoral threat to the DA.How does it reclaim its position as the main voice of the opposition?The next big test is the 2016 local government elections. Will the DA continue the growth it has enjoyed since 1994? Has it hit a ceiling? Maintaining growth will be the challenge of its new leaders.In her resignation announcement, Zille was absolutely right on one issue: "South Africa is in a race against time to save the constitution."This, plus the stalled economy and rising unemployment, are the three key issues facing our country today. It is clear that the governing ANC does not see the depth of these challenges hence, for example, its assault on the public protector, the Hawks, the National Prosecuting Authority and other institutions.The question is whether the new leaders the DA will elect on May 9 have the ability to convince ordinary South Africans that they can handle these challenges.The landscape has changed dramatically since Zille took over in 2007 and they will have to fashion a new vision for a new set of challenges...