Tony Abbott is being good in this campaign, certainly so far, even to the point of praising the government’s superannuation changes when, as prime minister, he was totally opposed to any reform.

But his former chief of staff Peta Credlin delivered what surely will be one of the most-remembered cut-through lines of this campaign, when she dubbed Malcolm Turnbull “Mr Harbourside Mansion”.

For the duration of the election Credlin is a commentator on Sky. It’s a network that encourages strong opinions, so the sharper her observations the better they’ll like it. Obviously Credlin brings enormous experience and insight to her temporary new job. If she is to do it well, she has to be frank and not pull her punches.

But in the political world, she will be judged not as just another commentator but as a player. Fairly or unfairly, some will believe she has another agenda – that she can and will say what the former prime minister can’t if he wants to keep his hands clean.

Credlin’s memorable description was delivered when she was commenting on Turnbull’s bad day in Lindsay when MP Fiona Scott was grilled about how she voted in the leadership ballot. There has been anger in certain grassroots Liberal circles that she supported Turnbull – although, standing beside the prime minister, she refused to confirm he had got her vote.

After their awkward news conference, Turnbull cancelled a planned street walk. The official reason given was that the timetable had slipped.

Credlin criticised the Turnbull caravan for being “flat-footed”. “I would’ve thought, particularly with the prime minister there, they might have been a bit more agile, a bit more nimble.” If Scott wasn’t pump-primed they should have moved the visit, Credlin said.

Ouch. One of Turnbull’s favourite words, “agile”, transformed into a knife.

Cancelling the walk was a bad move, in Credlin’s opinion. “If it’s known that you were going to do a street walk in Penrith, the last thing you want to do, Mr Harbourside Mansion, is look like you don’t know and you’re not welcome in western Sydney.”

Abbott had a special affinity with Lindsay, where he had campaigned hard. He was a friend of former member Jackie Kelly and in the 2013 election made his much-talked-about “sex appeal” comment about Scott. Liberals in his electorate of Warringah used to help Lindsay Liberals – though no more.

The moniker Credlin gave Turnbull was revealing as well as damaging. It’s quite probably the way Abbott and Credlin would privately regard Turnbull. Although Abbott has been comfortably middle class all his life, Turnbull’s world is vastly different.

“Mr Harbourside Mansion” brings together in one image everything Labor would like to conjure up about Turnbull – the wealthy man living in circumstances greatly removed from ordinary people, and out of touch with their thinking and needs. The use of “Mr” gives a special twist.

It is the sort of insult of which Paul Keating would have been proud.