It was Dunne’s basic goodness that did for him. Politicians leak all the time. Helen Clark was masterful. But they don’t get caught. That’s because they know what they’re doing.
You certainly don’t use your Parliamentary email. You don’t discuss with a journalist the possibility of leaking. That gives them the power, either through error or design, to get you sacked.
If you’re going to leak, leak; don’t leave your fingerprints all over it.
The leaking, too, has to have a point: it advances your cause, knocks an enemy off course, distracts the media from your own problems, or helps set the agenda. The leak was of no political benefit to Dunne whatsoever.
Most leaks are to disadvantage the other side. This leak disadvantaged the Government he is part of, and didn’t help Dunne at all. A few people think that maybe Dunne wasn’t the leaker – that he just helped Vance confirm the story and she had a second source. But personally I go with Occam’s razor.