Finally, Malcolm Turnbull has had something run his way.

Getting to this point has been an unnecessarily costly process in which mollifying fetid Coalition internals has taken priority over a wider public interest.

The piecemeal postal survey, a camel created from the political ruins of cynical delay and moral recalcitrance, was the brainchild of Peter Dutton.

No fan of change, the right-wing Immigration Minister was nonetheless adroit enough to understand that Turnbull - and therefore his government - could simply not go to the next election proposing the same plebiscite negation it carried like a dead weight through the last poll. Not when Labor would be offering an immediate parliamentary path forward.

Dutton intends to vote no but, to his credit, has promised to reflect the majority public will in a subsequent parliamentary vote.

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Some of his colleagues - furious advocates of the plebiscite, the survey, or presumably any measure to stall the change - have not matched that promise.

For Turnbull, whose year has been characterised by one setback after another, judicial rejection of the voluntary mail-in would have been serious - sending the government back to square one, and Turnbull himself to the backbench unless he was careful. 

There has been much pseudo-democratic posturing and strategic miscalculation on both sides, but for the defeated High Court petitioners, Turnbull's win can become theirs also.

That's because the imperative for them and for the federal government has suddenly aligned: to rescue the credibility of what is, on the face of it, an abysmal process. 

That means moving heaven and earth to ensure the mail-in achieves a respectable participation rate and a clear positive result.

Same-sex couples are on a quest for legal and social equality. Failure would not end their hopes but could set them back by years. In Canberra the agitation would continue.

Turnbull is delusional if he thinks he can sit this out - pledging the support of him and his wife Lucy, but doing little more. 

Rather, he should recognise the game-changing opportunity this offers him to be the Prime Minister who delivers a popular, overdue reform. It would even go some way to assuaging the damage of past betrayals.

Besides, consider the alternative. If marriage equality fails from here, Turnbull will get the blame anyway.