General elections are significant events with many ramifications.
They not only determine (in most cases) which party will form the government - they also set the political agenda for the winners and losers over the three years until the next election.
Particularly in cases where the government changes, that agenda will be dominated by the new challenges created for the major parties by the changed role they must take up.
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For the winners, especially if they have been out of government for some time, there will be a host of new challenges. As Labour is discovering in the wake of its 2017 success, they must take over governing the country without a core of experienced former ministers.
As I know from my own former political experience, being in opposition is a very different matter from shouldering the responsibilities of government.
In opposition, you can pick and choose your issues – and the choice is usually an easy one. You can head straight for those issues where the government is under pressure or where public opinion is demanding new answers to high-profile problems.
There is less need than there is in government to have an answer to every question.
In government, however, everything you do, or fail to do, is rightly assumed to be on behalf of the government. You cannot say, if caught out doing or saying something that you would rather keep out of the public domain, "that's my business".
Jacinda Ardern has had an uncomfortable few weeks largely because of mistakes made by one or two ministers who are enjoying their new status but who have not realised that new standards of responsibility are also expected.
The good news for her is that the passage of time, and growing experience about what is required, should remedy these failings – and Ardern herself will no doubt learn lessons as to the best way of dealing with ministers who fall short.
But the change of role is not just a problem for Labour. The transition for National – in its case from government to opposition – is, if anything, even more difficult.
It has suddenly lost the status that comes with calling the shots and being in charge, and has lost not just the perks of office (such as the chauffeur-driven limousines) but more importantly the advice and support of usually highly competent civil servants.
National MPs need to rely much more on their own judgments as to what points to make and how a particular issue is likely to develop. They have to work much harder to set the agenda – journalists no longer hang on their every word.
And they have to strike that difficult balance between holding the government to account and seeming to be perpetual nit-pickers and nay-sayers – all the while trying to persuade the voters, with an eye on the next election, that they could do so much better a job next time.
And, as in the case at present, they might also have to bear the burden of skeletons in their cupboard coming to light, as issues and problems that had previously been buried far away from the public gaze get an airing.
There is a further problem for National. A general election defeat, leading to the loss of the government benches, can often mean a number of long-serving members will call it a day, finding little reason to stick around in opposition.
And so it has proved with National this time.
With the departure of Bill English and Steven Joyce (Jonathan Coleman may not count for this purpose), National has lost a good deal of experience and ballast. It is not just Labour that needs to rebuild in terms of experience.
As it faces up to the twin challenges of being an effective opposition and getting fighting fit to contest the next election, National is suddenly looking somewhat lightweight.
It is not just the loss of its heavyweights but the fact Simon Bridges has yet to make much of an impression – let alone a favourable one - that leaves the party looking a little short of firepower.
New governments usually find it easy to grow into the role – it's not so easy for recently defeated oppositions.