It’s great fun (well, the Canberra version of fun) trying to work out why certain stories explode into god almighty messes.

Bronwyn Bishop’s helicopter debacle is one such story. When the story first blew up (as helicopters are wont to do), Bishop realised the danger almost immediately and paid back the taxpayer money she’d foolishly used for her little joyride.

At that moment the story might have gone away.

The first question is: why didn’t Liberal strategists see the storm coming? One of the cardinal rules of politics is to minimise damage: if you know something is going to end up a disaster, a quick and clean cut is the best approach. Prevention, always, is preferable to cure. If Bishop had been sacked weeks ago, we would have stopped talking about her weeks ago.

But the strategists had their reasons. Tony Abbott, both before he became prime minister and since, has had to repay expenses – in one case seven years after the fact. Nor was he the first prime minister to do so. If a PM could get away with it, then it was reasonable to think perhaps a lowly Speaker could.

They would also have been thinking of the damage that any sacking does to a government. Prime ministers are always aware of the precedents they might set – every resignation makes the Opposition’s next call for a resignation more plausible – and of the signals they send to their troops about standing by each other when times are tough (because that message cuts both ways).

But the strategists (and the PM, and Bishop) got unlucky. The story didn’t go away – spectacularly so. Why not?

The first reason should have been obvious: the colour. It’s one thing to have to pay back taxpayer funding for undertaking a book tour (Abbott). Silly, but drab. The story does not excite. But a helicopter is symbolically awesome: with one image it speaks of the entire armoury of luxuries available to MPs, and unavailable to most ordinary humans.

The second was foreseeable, though not guaranteed. Labor acted quickly, foraging for tidbits to provide to a hungry press pack, referring Bishop to the police and foreshadowing that it would move a motion of no confidence as soon as parliament returned.

The third, also foreseeable though not guaranteed, was Bishop’s clumsiness. She should have apologised. She should have voluntarily paid back anything else even mildly questionable immediately. Instead, she gave a press conference that provoked further outrage.

The fourth: it turns out Bishop has made a few controversial decisions about travel expenses over the years. It’s that pattern of behaviour which is now slowly dragging her down to political earth. Her attempts to excuse some of those trips by saying she was meeting with unspecified people make her look ridiculous.

But it’s the fifth and sixth I find most interesting, because they are, to a large extent, a matter of timing, and therefore of luck. Some MPs have survived much worse crises than Bishop because their errors happened, happily for them, to be discovered during more fortuitous times.

The fifth, then, is the state of the polls. Nine days ago I wrote that while loyalty was important “there is always a tipping point, the moment that MPs’ enthusiasm for loyalty is overshadowed by their concern about polling numbers.” A week is a long time in politics, and nine days is, obviously, just very slightly longer. There is only so much of this story that a low-polling government and prime minister can stand.

The sixth is the particular size of the scalp that Bishop represents. A prime minister may be incredibly reluctant to sack a senior minister because that would be seen as a real blow. The media and the opposition may not care enough about a junior MP to go after them, the political equivalent of throwing a small fish back in the water.

But the Speaker is just significant enough to represent a real victory for Labor if they succeed in getting her sacked, and perhaps just insignificant enough for Tony Abbott to decide she’s no great loss.

Julie Bishop – or as I like to call her these days, The Lesser Known Bishop – made her namesake’s job just a little less tenable today by suggesting the Speaker was considering her position, and reminding her colleagues of the political vulnerability she represented: “I understand that the Labor Party will seek to use this to destabilise Question Time, for example, and I’m sure Speaker Bishop will take that into account as she considers her position.”

It was a slightly brave move, considering TLKB hasn’t been innocent of controversial use of travel entitlements. In 2011 she claimed $3445 to pay for flights home from a wedding in India (having flown over on Gina Rinehart’s private plane), saying she had several official meetings that justified the expenditure.

But her intervention is, nevertheless, significant. Scott Morrison also refused to defend BBish today. Both TLKB and Morrison are potential leadership contenders, should Abbott falter. Turnbull, the third of the contender troika, had his fun too.

When the three people most likely to replace you have a unified view on something, you have to have a very good reason to stand your ground. If the Speaker’s career ends in tears, today will stand as the beginning of the end.

Today’s links

• Penny Wong took on Cory Bernardi over same-sex marriage at the National Press Club. Michelle Grattan on gay marriage manoeuvrings and what Scott Morrison and Tony Abbott are up to. Conservative Liberal MPs are increasingly desperate in their arguments to stop same-sex marriage being legalised.
• The real stats on women in politics. Liberal MP Kelly O’Dwyer opposes quotas for female MPs in her party, suggesting targets are a better approach. Quotas vs targets is an important debate, but I thought Dwyer was kidding herself about the reality of the way her party operates when she said: “We are a grassroots organisation, we’re not like the Labor Party where you can stitch up factional deals between different factional warlords to determine who should be shoehorned into a particular seat.”
• More than 60% of voters did not think the carbon price had a significant impact on their power bills.
• The Adam Goodes booing debate is really heating up. There was this radio clash. Alan Jones got angry (though most of his points seem identical to those made by Miranda Devine and Rita Panahi on this issue).
• Paul Kelly on Labor’s new turnback morality.
• Add another voice to the chorus of perhaps-this-slow-economy-we-have-is-the-new-normal.
• The SMH reports Bill Shorten has flagged supporting increased transparency for political donations. That would be great, but his commitments sound pretty vague at this point. Tony Abbott has basically said no dice