As John Key exits stage centre undefeated and to much applause, the question becomes who will be bold enough to take up his mantle in the middle? As voters start shopping around, who's looking the part to succeed him? 

John Key's resignation is an immense shock in a year of immense shocks, but it also lays down a gauntlet to those who would be in government next year. The speculations about where we go from here are delicious, but we know for sure today that Key leaves as the most popular politician since perhaps Kirk or Muldoon in their pomp and the person who wants to lead after next year's election will have to define themselves in response to him and the political landscape he has carved out.

The question now is who will seize this moment. Who has the courage to be bold? Or, perhaps, the courage to hold their nerve? Because every political door is now open. This is a rare moment where just about anything is possible. And we'll get to find out just how substantial the Key magic really is. 

For National, does Key's endorsement of Bill English carry sufficient weight to sideline the potential challenges? Is the party as stable as it has looked under Key, or without the glue of his popularity, will the factions arise? Politicians only get so many chances to run for leadership, and even fewer to be Prime Minister. It will be an immense test of discipline to avoid a leadership race. Unless...

And this is where the speculation arises. Does English want the Prime Ministership on his CV regardless and does he even want to commit to another four years in harness? It's a risk, personally. Yes, there's the chance he could win and help National break the nine year rule, but history is against him. Certainly, he can claim as much credit for National's strengths as Key could. But he's also risking becoming a two-time loser. There's every chance that he, a bit like Phil Goff (or himself in 1992), might end up taking a loss for the team while they identify a long-term successor.

At least, he may think, like a Mike Moore or a Jenny Shipley, he could claim the title, even if it is at the end of another's dominant era. He could still make his mark and have his name on the board. 

Part of that mark could be preparing the next generation. While the received wisdom tonight seems to be that he could bring Steven Joyce in as either deputy and/or finance, how much more forward thinking to bring the next generation into such roles? Why not make Amy Adams deputy and Simon Bridges finance? It says rejuvenation to the public, keeps them in his camp (for now at least), and readies the party, should he lose next year. (And, let's be honest, it keep Judith Collins at bay, something he will want to do).

The final question, should English step up, is whether he should or could go to the country. There's no constitutional justification, no need to steady the ship of state. But he could potentially argue that he wants a new mandate, thereby riding the Key wave before it crashes on the beach of public apathy.

When Winston Peters walked out on the National-New Zealand First coalition, Shipley chose stability over political risk. She decided to see out the term, perhaps for the best of reasons. But sometimes political opportunism works and, while it doesn't seem in his nature, English might be tempted to have a crack. 

Of course, it may not be a decision English gets to make. Will other potential successors, Collins included, be willing to wait? Or, like Mike Moore in 1993, might they be willing to take a short run at the job a) for the party's sake and b) just so they can have the top job on their resume? This bus only comes by so often.

Collins - and perhaps Bennett - has to consider whether they're best placed to seize the ring as it flies by or wait for a potential loss next year and come in with a fresh three year run from opposition. The phones will be running hot as Collins figures out how brave she wants to be at this stage.

But perhaps the biggest question of political courage lies at the door of Andrew Little. Arguably the luckiest man in New Zealand politics, he came to the Labour leadership at a time when another change was simply unimaginable and now he's been handed the political gift of a lifetime.

Has he got the nous and the hunger to see it for what it is and grab his chance. There's every possibility National's polls could start to slide - even plummet - without Key. Any successor will pale in comparison with the public. Suddenly, that magic figure of 35 percent for Labour doesn't look so impossible. 

But there's no law of gravity that says the soft National vote has to go to Labour. Winston Peters has a chance - if a somewhat slim one - or taking New Zealand First to new heights. So Little has to act decisively to see off Peters.

That's not what Labour's left wants to hear. They'll be arguing for the chance to win an election on their terms. That would be to look a gift horse in the mouth. 

This is Little's chance to grab the centre, if he heeds the call. Labour's angst about how much space to leave on its left and how much to cleave to the centre has been decided for it. Leave the left to the Greens; that does them little harm. They now have an unparalleled chance to regain relevance in the soft middle, to speak to the old Labour strivers who just want to see them and theirs doing a bit better year to year and know that their government isn't going to squander their hard work.

Maybe Labour could play National's trick, and steal some of its policies. Labour won't want to see it this way, but I'm going to say it any way. The coming weeks is a job interview for who gets to be Key's successor. (I said successor, not mimic). And Little is a candidate. Especially against Collins, but even against English. 

Who can find the words and make the connection? Because suddenly voters are going to be shopping around, looking at the same political goods in the new light. 

Little needs to accept that Key has been popular and has delivered policies a winning bloc of kiwis like. Little should not be so proud as to try to take Key's mantle in the middle. He will have plenty of time in office to paint it as red as he likes, but he's got to win first.

After almost nine years, and now without Key, some voters will be will willing to detach from National. But if Little genuinely thinks Mt Roskill or any other indicators suggest a sweeping mood for change, he's likely to squander this moment. 

Roskill was more than else a local result; a vote for candidates and issues, not parties. If Labour misreads that, this moment will pass them by. 

Little's goal now has to be to get big enough to lead a two party coalition. And, as hard as this will be for the Greens to hear, the second party is likely to be New Zealand First. Peters' biggest reluctance to change the government next year would be down to installing a party well behind in second place and ruling with (or being)  a third wheel. That's not his style. 

So Little should be looking to bring National down to 40, maybe a bit less, and then to be within the margin of error. Then, it's all on.

So the question tonight - as the MPs phone each other and make some of the biggest decisions of their careers - is who will be bold and seize this moment of change.