Simon Bridges had no sooner warmed the leather in the Opposition Leader's chair than he was declared irrelevant by one columnist.

It was a sentiment that many others shared for different reasons.

Some were annoyed because Bill English had gone, others because Bridges was not Judith Collins, or Steven Joyce, and an awful lot more because he was not Jacinda Ardern.

The honeymoon continues for Ardern who, it seems, no longer conducts Government business but conducts charm offensives: last week in Australia, this week in the Pacific and next week with five million viewers of NBC's Today show in the United States.

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Bridges has been more of a curiosity since his election as National Party leader. People have stopped and looked, gained a first impression about his ambition, voice, hair or Maoriness, and carried on. It is pretty clear he is not going to get a honeymoon.

Like the new proprietor of a successful bakery, he has inherited the goodwill of a sizeable chunk of the previous guy's customers. But they are not going to give him loyalty without what he produces.

His first crucial move, to make Amy Adams the shadow finance minister, was well signalled.

When he says she would have been his choice in finance even if she had not been a leadership contender it is easy to believe.

Adams is the third high-flying woman to emerge from the Selwyn area in National, after former Finance Minister Ruth Richardson and former Prime Minister Jenny Shipley.

She talks at a crisp clip with a slight plum in her mouth that she almost certainly didn't pick up at Rangitoto College.

Adams exudes efficiency and discipline. She had a reputation for grasping detail quickly and getting things done when she was a senior minister in Government across a broad range of portfolios including social investment.

She will not white-ant Bridges, despite missing out on the leadership. She is trustworthy and clever.

But she will need to do some serious homework to get anywhere near the fluency that English or Joyce had in finance – or the proficiency that Finance Minister Robertson has already acquired through incumbency.

It would be a mistake for her to view Robertson as an easy target or to give the impression she knows more than him - she can tend to come across as arrogant.

She has been an Associate Finance Minister although that was not immediately obvious in her contribution to a debate on the 2018 Budget Policy Statement (BPS) 10 days ago.

She may have been called upon to speak with no notice and without preparation. That is the only explanation for why there were many basic errors.

She suggested there had been no provision in the Government books to fund the spending promises other than the costs of the 100-day plan in the Half Year Fiscal and Economic Update (a net $5 billion over five years) and that they would be funded by adding to the projected $70 billion debt.

It is true that the costs of the other polices were not set out – that will happen in the May Budget. But they will be funded out of operating and capital allowances for new spending which were specified in the Budget Policy Statement: for operating $2.6 billion in 2019, and $1.875 billion per Budget thereafter, and for capital $3.4 billion in 2018 and 2019, $3.1 billion in 2020, and $2.7 billion thereafter.

It makes the Government sound awash with cash when it is not. It will be a tight three years. The enormous cost pressures that Labour and New Zealand First will face after raising expectations will be a constant refrain for Adams in her new role.

But if Adams is to gain credibility in the role, it has to be on reliable fact, not alternative fact.

She said there were 34 pages in the Budget Policy Statement identified by Treasury as un-costed fiscal risk. The BPS is a political statement by the Minister of Finance, Grant Robertson, and is only 20 pages long. Yes, there are 34 policy-changes risks identified in the Treasury's HYEFU document and other cost pressures but identifying such un-costed fiscal risks has been standard practice for years – and there are always more in the update following an election because there are so many policy changes.

Adams needs to know what she doesn't know. She has to know what is in the books and what is not before she starts engaging.

She needs to lock herself in a room for a couple of weeks with a pile of policy documents from Labour, New Zealand First and the Greens and a pile of Treasury documents and know exactly where the vulnerabilities of the Government sit.

Being on top of her portfolio and illustrating fundamental differences in approach will be more important than making "gotcha" hits against the Finance Minister in the House.

Amy Adams vs Grant Robertson is a much more even match than Robertson faced three years ago.

Robertson started out raw in the job against English who had been minister for six years and had got the books back in the black with an agenda of restraint rather than austerity.

English became an even more difficult target for Labour by out-Labouring them on rises in social welfare benefits, a strong social justice agenda and a massive pay equity settlement.

There are few parallels for Adams though. Robertson was in a party that had been trounced at the election and he set up a vehicle, the Future of Work Commission, that gave a purpose to his engagement with business and sector groups and a body of work from which to draw up new policies.

Adams has to engage similarly but her mission will be to come up with some appealing new policies without tampering too much with a successful formula or annoying the party base. It will be a hard grind.

If being Opposition Leader is the worst job in politics, being Opposition finance spokesperson is possibly the second worst. Adams will have to fight for relevancy and one thing is for certain, she won't be getting any honeymoon.