Or a worse one begins.

The Prime Minister awaits the people's verdict in Bennelong fully aware of the stakes. Either John Alexander holds the normally safe seat against Labor's Kristina Keneally, or Alexander succumbs, ending his parliamentary career and more or less sealing Turnbull's decline into the bargain.

An anti-Liberal swing is expected, but Labor's task has always been gargantuan. Doubling the usual byelection backlash to nearly 10 per cent is ambitious. Especially where the likeable incumbent is running again after being ruled out on a technicality. Voters hate such finicky circumstances and some express sympathy at the ballot box rather than the normal anger when a byelection is caused by a voluntary resignation. Take New England just weeks ago.

For Bill Shorten the stakes are also higher than some imagine. The Opposition Leader's handpicked candidate was an inspired choice because in this race, there was no time for profile-building. He needed a candidate with instant recognition and the articulate, intelligent Keneally unquestionably brought that. Unfortunately she also brought baggage via her past associations, however reluctant they'd been, with nefarious NSW Labor characters now doing time.

Both leaders have been on the ground in Bennelong repeatedly. Shorten the more so. He will be hoping for a win but will be chuffed with any improvement above 5 or 6 per cent. The Labor leader's had a good year but recent errors on citizenship and Sam Dastyari have harmed Labor's chances. For Shorten there would be no escaping criticism from a poor outcome.

Bennelong is crucial.

Clearly Turnbull is wealthy enough to buy himself a new Aston - as car enthusiasts abbreviate the classic British marque.

But it is no luxury sportscar Turnbull covets this Christmas but a vehicle to political safety. In 2001, this was the Liberals' Aston byelection victory in oddly similar circumstances.

Remember John Howard's relief the next morning: "I believe that the government is well and truly back in the game. If there were an unstoppable momentum for Labor to win the federal election, they'd have rolled us over in Aston."

That proved right.