Despite that, NSW Premier Gladys Berejkilian was quick to paint the Coalition as underdogs in the seat. Ms McKay pointed to decades of electoral history in disputing that claim. On Monday the field contesting who will represent the coal-dominated area in Macquarie Street became a bit clearer.

Nurse and businesswoman Sue Gilroy has been officially named the Shooters, Fishers and Farmers Party contender. Ms Gilroy, the head of the Singleton Chamber of Commerce, will be hopeful of reaping the benefits of any backlash toward the Nationals related to the allegations against Mr Johnsen, which he stringently denies.

One Nation are yet to name their candidate, but it will not be the party's former federal candidate in Hunter Stuart Bonds. Mr Bonds has not ruled out a tilt at the state seat in May after a split with his erstwhile party over industrial relations that proved irreconcilable. A week ago the Nationals named construction engineer David Layzell as their hope to hold onto the party's 2.2 per cent margin at the 2019 election. Now Labor too has entered the fray, nominating Jeff Drayton for the contest that veered into the politics of coal and mining before many Sydney-based politicians had even been able to join the campaigns.

Prime Minister Malcolm Turnbull was the first casualty, losing his appointment to a climate advisory board when it became what the Premier described as a "distraction" in the wake of his comments supporting a moratorium on new mines. He is certainly not the last given only one candidate can take up the mantle of representing constituents in the seat, which was redrawn in 2015.

But by-elections can be unpredictable things, offering an outlet for frustration as well as a flashpoint for local issues. How much weight the circumstances in which this one was called, and for that matter the future prospects of the coal industry in its heartland, will bring to bear upon the electorate remains an open question.

The only definitive answers will come at the ballot box next month.