Suddenly, every Labour Party proposal has to be taken very seriously. A plan to run light rail trams from the Wynyard Quarter, through the CBD and down Dominion Rd all the way to Auckland Airport is no longer just a fiction of urban planners' imagination.
The surge of interest in Jacinda Ardern, though yet to be tested in a proper poll, means it is quite possibly the next Government will finance the project.
Indeed the new leader has had the courage to tell Auckland car drivers they will pay an extra 10c a litre for petrol to help pay for the tram line.
However it is to be financed, it amounts to a substantial national investment. When a project on this scale is proposed, the public should be spare a thought for the economy. Ours is not a big economy like most of those that have installed light rail in their metropolitan centres.
A small economy is easily damaged by investment that generates a poor return compared to alternatives.
Any objective evaluation of the merits of light rail in a city the size and shape of Auckland needs to explain why they would be better value for money than the bus services the presently serve Mt Albert, Mt Roskill and Mangere.
As for going to the airport, Labour will need to explain how this proposal stacks up against a much shorter rail connection to the main trunk line at Puhinui, or indeed the road journey that has just been improved by the Waterview Tunnels, completing the urban motorway network at long last.
Aucklanders in the west and north of the city and the CBD have just begun to enjoy the luxury of motorway nearly all the way to the airport.
They may take some convincing that a $3b light rail service is worth an additional tax on their petrol, or indeed that such a service is practical.
Light rail through the CBD and down Dominion Rd would be running on streets, stopping frequently at traffic lights as well as to pick up passengers. Labour needs to explain how this would work.
Would travellers to or from the airport be on the same trams that would be stopping every two blocks for passengers? If so, it would seem a painfully long journey by comparison to car, shuttle or a bus on the new motorway.
And what about the baggage that air travellers haul? If airport travellers are to have an express service with fewer stops, the route would need to be double tracked, leaving little room for other traffic. Is that the plan?
Labour sometimes refers to light rail as "rapid transit" but there is nothing rapid about rail on the streets, whether its is the smooth, quiet rolling stock of modern design or the rattling trams of yesteryear.
Rapid transit is a dedicated route such as a subway or busway, it is not a transport mode that has to share the road.
This policy served the party's need for its new leader to announce something bold and definitive.
Light rail is perfect for that purpose, it is flash and fashionable. But whether it could pass an economic test is the question voters should consider.