The worst thing a Government can do to the Opposition is to ignore it, and consign it to irrelevancy, but not so this week.

From the moment the latest Colmar Brunton political poll was published on 1 News on Monday, Labour was on the case of Simon Bridges, the new National Party leader.

Bridges polled only 10 per cent as preferred Prime Minister to the incumbent, Jacinda Ardern on 37 per cent.

But Labour has been behaving as though he was a clear and present danger.

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Emissaries from the Beehive were dispatched to the Press Gallery to reinforce the point that not only that the gap between Ardern and Bridges 27 points, but that former leader Bill English had done way better against Ardern at the start of this year.

Not only that, they had further ammo targeting Bridges, who took over from English almost eight weeks ago: Bridges' debut rating of 10 per cent compared poorly to John Key's first rating as National Party leader at 27 per cent in 2006, and Jacinda Ardern's first rating as Labour leader in at 26 per cent in 2017.

Labour's home-grown leadership losers were not spared from the campaign to reinforce the apparently hopeless case of Simon Bridges - he had done even worse on debut than David Cunliffe, David Shearer and Andrew Little - historic data helpfully produced by Labour showed.

Acting Prime Minister Kelvin Davis was similarly briefed for his media messaging on Tuesday – comparing Bridges' debut to Ardern's.

Davis went more personal, saying Bridges own ego would have placed him a lot higher than 10 per cent. Bridges should be disappointed and embarrassed, Davis told Newstalk ZB's Mike Hosking.

If Bridges is doing so badly as preferred Prime Minister why is Labour treating him as a threat in such a concerted effort?

Despite the Labour coalition and its parties holding a majority in the poll, there was much for National to be pleased about and a lot for Labour to be concerned about – namely the party vote.

National's party vote support has remained virtually unmoved since the election despite the loss of a highly respected leader in Bill English, a five-way leadership contest, and in the first term of a very popular new Prime Minister.

Until the series of mishaps and controversies in the Government over the past five weeks, National had been expecting to take a hit in the polls, perhaps to the high 30s.

But brand National is stronger than they thought and the Jacinda effect has not been as strong - her own rating having fallen four points.

Historic comparisons are not necessarily valid either when it comes to comparing leader popularity to party popularity. The variables include personality, the number of prominent leaders, the time in the electoral cycle and how long the leader has been in place.

Former National Prime Minister Jim Bolger, example, won the 1993 election even though he was less popular than Labour's Mike Moore.

Former Labour leader Helen Clark was on 2 per cent popularity in May 1995, well after gaining the Labour leadership in November 1993, although she gained popularity before becoming Prime Minister in 1999, but only to the low 20s.

Clark eventually made it to the 50s as preferred Prime Minister in early 2002, when the Alliance was falling apart, as did her successor as Prime Minister, John Key.

Comparisons between Bridges and Key are not valid because Key gained the leadership in the third term of the Labour Government.

Bridges has a long way to go to create a strong brand identity as National leader. He had a half-hearted attempt last week at his old school, Rutherford College.

But Labour must be worried that if National's support has held up without Bridges having done so, then he really does present a real threat if he succeeds in establishing himself more positively.

That is reason enough for Labour to try to undermine him before he actually starts, by painting him as a loser before he has even begun.