For many years now, Australian political scientists have pointed out that that established partisan allegiance is in decline. In 1967, 36% of Coalition supporters and 32% of Labor voters reported lifetime voting for their side. At the 2022 election, the Australian Election Study found the figures to be 16% and 12%.

These changes help to explain the rising support for independents and minor parties at federal elections; they now take about a third of the primary vote.

So much for voters. What about for politicians? Of course, there have always been plenty of parliamentarians who had an earlier stint as a member of some other party before landing in the one that sent them into parliament. Brendan Nelson was in the Labor Party before he was Liberal. John Gorton was Country Party before he was Liberal. Adam Bandt was Labor before he was Green. And so on. We are all entitled to change our minds, even if switching political parties was once closer to changing football teams - a habit that immediately arouses suspicion in a sports-loving nation.

Senator Dorinda Cox's switch from the Greens to the Labor Party was apparently a homecoming, according to Cox. She was once a Labor Party member, she said. Last week, she was criticising the party over its approval of Woodside's Northwest Shelf gas project. This week, she finds Labor's values aligned with her own.

Of course, her defection has been accompanied by a steady leaking of little details of her Greens career, such as an excoriation of the Labor Party, in her application to run for the Greens, when she said the ALP patronised "women and people of colour" and cared more about its donors than members.

That's politics, but it's a democratic deficit that senators elected as part of a Senate team, in a system that has facilitated above-the-line voting since 1984, can sit for years afterwards in the parliament as a member of another party.

But good luck in getting up a constitutional change, via referendum, to change that.

Still, it is easy to understand how such nimbleness breeds cynicism about political parties. Another perspective might be that the fluidity of allegiance out in the electorate has come to inhabit the political class itself.

All the same, defections from one party to another are quite rare these days in federal politics, at least after one is sitting in parliament. But defections from a party to sit as an independent are not and some, such as Bob Katter, have managed to build successful political careers outside the parties.

One who did not was was Julia Banks, the Liberal member for Chisholm, who announced she would not be seeking re-election and then left the party for the crossbench in the wake of Scott Morrison's ascension to the leadership in 2018. Banks complained of bullying and intimidation within the Liberal Party and the wider parliament, and wrote a book on her experiences. She subsequently failed to gain election as an independent in another seat.

There were several defectors in the last parliament. A House of Representatives crossbench that began at 16 had reached 19 by the end, with the defections of two Liberals (Russell Broadbent and Ian Goodenough, both after losing preselection) and one National, Andrew Gee, the latter over his party's opposition to the Voice. Only Gee has lived politically to tell the tale, winning Calare as an Independent, as Peter Andren did before him.

Defections from minor and microparties are especially common, based as they often are on a high-profile leader and lacking traditions of party discipline or solid structures of organisational governance. Jacqui Lambie began as a Palmer United Party senator. Tammy Tyrrell began as a Jacqui Lambie Network senator.

The biggest "defection" in modern Australian politics was that of Cheryl Kernot from the Australian Democrats to the Labor Party in 1997. It is easy, over a quarter of a century on, and with the Australian Democrats no longer in the Australian parliament, to underestimate what a big deal this was at the time.

Kernot was a rock star of a politician, leader of the Australian Democrats, and a national celebrity. But there are significant differences with Cox beyond Kernot's greater eminence. She resigned her Senate seat immediately and would win the marginal Brisbane seat of Dickson in the following year's election. Then, in 2001, she would lose it to a young and ambitious former policeman named Peter Dutton.

The experience was ultimately an unhappy one for Kernot: she believed that having recruited her into the ranks, the Labor Party - and its leader, Kim Beazley, did not know how to make the best use of her. She was also on the receiving end of some relentlessly negative and sometimes intrusive media coverage. And by her own admission, she made mistakes. The story of her career's unravelling is not straightforward. The role that gender played in it remains contentious.

Perhaps Kernot's experience would alone be sufficient to prompt second thoughts in anyone seeking to jump ship. There are, of course, older prohibitions. In the Labor Party, a defector was known as a "rat". Billy Hughes, the prime minister whose effort to introduce conscription in the first world war split the party, is the most famous of them.

"Rat" is not a word much heard these days, but it was thrown around a bit when Senator Fatima Payman defected in 2024, and applied more seriously in 1996 to Labor Senator Mal Colston when he resigned from the Labor Party in exchange for the deputy presidency of the Senate.

The best historical example of a defection being good for your career is that of Joe Lyons, who ratted on Labor in 1931 to lead a new party called the United Australia Party, a switch engineered by a small group of influential businessmen. The circumstances - the Great Depression, real fear of civil violence, and the disintegration of a federal Labor government - were highly unusual.

More commonly, defection is a bad career move. Most of the Labor politicians who went over to the breakaway anti-communist Democratic Labor Party (DLP) in the mid-1950s found themselves out of parliament and looking for a new job. Stan Keon, one of those flying high ahead of the split, even occasionally mentioned - unrealistically - as a possible future prime minister, would run a Melbourne wine shop. Others, such as Vince Gair, Queensland Labor premier, lived to fight another day as a DLP senator (and ambassador to Ireland).

Cox has three years left of her senate term. After that, she will be at the mercy of the Labor Party. Labor won three Senate seats at the 2022 half-Senate election in Western Australia and perhaps it could do so again. On that occasion, in a surprise victory, the third place went to the young up-and-coming union organiser, Fatima Payman.