I don't understand privacy/publicity rights laws in Australia, so have no idea if what you are saying is correct there.

The conversation here has been about US law, and one of our members quoting a British photographer - not lawyer - to try to make a false point about US law.

In the US, the model would not need a model release (the politician would not need a model release) to use a photo of themselves in advertising for themselves.  As I mentioned there may be copyright problems, but that's a separate issue.

I the US it's entirely likely that a model release would not be needed to use a picture of an opposing politician in a political campaign.  I'd guess it is not needed, but I haven't looked into it to make sure.