Whatever might be said about its merits as public policy, yesterday’s announcement that the new fleet of 12 submarines would be built in South Australia signals a dramatic change in that state’s political fortunes.

As the Abbott government’s guns blazed in the wake of its election victory in September 2013, it offered no indication of sentimentality about the challenges the state faced in managing the decline of its manufacturing and industrial base.

Not only was the government ideologically disposed to the view that the best medicine was tough medicine, the then-prime minister and his brains trust clearly felt emboldened by the state’s apparent lack of electoral clout.

Of the six seats the Liberals hold in South Australia, the only one with a margin of less than 7% is the western Adelaide seat of Hindmarsh, where Matt Williams unseated Labor’s Steve Georganas at the 2013 election.

The next seats along on the pendulum are Boothby (margin 7.1%), which Labor hasn’t held since 1949, and Christopher Pyne’s seat of Sturt (10.1%), which Labor hasn’t held since 1972.

So it was that the Abbott government remained aloof as Holden announced the end of its Australian car manufacturing operations, and the government set about softening the state up for the likelihood that submarine construction would be lost to Japan.

No doubt then-defence minister David Johnston went beyond the sanctioned government line in declaring he would not trust the Adelaide-based and government-owned shipbuilder ASC to “build a canoe”, but South Australians would have been only too alert to the fact that the sentiment did not appear out of thin air.

In the light of yesterday’s news that the $50 billion project will proceed on local soil early next decade, the pleasure felt by South Australians at the change of heart concerning their state’s manufacturing prowess will be tempered by healthy cynicism as to what might have caused it.

Try though the government might to deny it, a big part of the answer is the Nick Xenophon Team and the damage it threatened to do if it had been able to bang the drum on the issue in the looming election campaign.

The latent power of Xenophon’s new party was indicated by his own performance at the 2013 election, when fully a quarter of South Australia’s voters supported him in the Senate.

Under the new Senate electoral rules, that would certainly win his party three of the state’s 12 Senate seats at a double dissolution election.

However, the nuclear scenario would involve a replication of that result in the lower house, as the Xenophon Senate ticket outpolled at least one major party in all but one of the state’s 11 seats in 2013, and outpolled both of them in Boothby and Makin.

In any circumstance where the NXT outpolled a major party in the lower house, it would stand to receive nearly all of that party’s preferences, making it very likely it would ride home to victory over the other major party at the final count.

Modelling by electoral number cruncher Kevin Bonham suggests the NXT could perhaps pick up a seat with 17% of the statewide vote; could maybe make that two with 20%; and could blow things right open with 25%, winning as many as six to eight seats.

Opinion polling has painted a mixed picture as to the likelihood of such a result.

A Galaxy poll of state voting intention in February had the party at 24%, which gave a strong indication that support for Xenophon personally was increasingly becoming transferable to his party brand.

Roy Morgan’s polling has had the party’s federal vote in South Australia ranging from 15% to 22.5%, the latter result having been obtained in its most recent poll.

Polls conducted by ReachTEL for the Australian Manufacturing Workers Union and the Australia Institute have been less dramatic, suggesting the party’s lower house vote to be in the high teens, but such results may be scratching the surface of what the party can achieve after publicising its existence in the full glare of an election campaign — particularly with an issue as immense as a $50 billion submarine construction program to fight on.

Even if the NXT’s share of the vote was relatively modest, the Liberals would have grave fears of it winning the seat of Mayo from beleaguered Liberal member Jamie Briggs.

Then there is the potential for havoc the party might wield through its preference recommendations, which could be used to finish off Christopher Pyne in Sturt even if the party is unable to win the seat itself.

Beyond the enormous public policy implications of yesterday’s announcement, there could be an even more important lesson about the perils of taking voters for granted based on the crude electoral calculations that appeared to guide the government under Tony Abbott.

As party loyalties decline, it’s no longer the case that the major players only have each other to worry about.

Much as the government might hope that Senate electoral reform will cause this sentiment to fracture and dissipate among a scattered array of micro-parties, it seems at least as likely that discontented voters will adapt to the new environment in more effective ways.

Without a vote being cast, Xenophon may already have shown the way by demonstrating how voters can leverage support for regional mavericks into tangible benefits for their states.

That’s a lesson that’s likely to be noted well beyond the borders of South Australia.