How Lidia Thorpe leaving the Greens will impact the Voice to Parliament referendum, black sovereignty movement

The Greens bent over backwards to keep Thorpe within the party. Their leader Adam Bandt promised her a conscience vote on the Voice referendum and even her continuance as party spokeswoman on First Nations. That huge compromise, always going to be messy, was not enough.

Echoing many other independents before her Thorpe argued that she would now be able to "speak freely on all issues from a sovereign perspective without being constrained by portfolios and agreed party positions". That draws a line in the sand between all political parties and independents and parties should be worried that the idea doesn't catch on.

Already Andrew Gee MP has left the Nationals over their opposition to the Voice and who knows what might happen when the Liberals finally land on a position. There are many possibilities for further political party fragmentation.

What difference Thorpe's decision makes to the politics of the referendum depends on how big and united the black sovereignty movement is and how it acts towards the Voice.

Thorpe spoke of a "strong grassroots black sovereignty movement, full of staunch and committed warriors". A minority of Australians, Indigenous and non-Indigenous, support black sovereignty and speak of stolen land and sovereignty never ceded as Thorpe does. I've noticed it among young people and during some welcome to country acknowledgements, for instance. Some Australia Day marches voiced the same sentiment. Supporters of a Treaty might count themselves as part of this movement.

But many such people already support the Greens, the Labor Party or Teal independents. As Thorpe herself acknowledged in her parting statement most Greens voters support the Voice and want to vote "Yes". She can't count on their backing. Indeed she has left open voting for the Voice herself. The implication of her departure is uncertain.

The greatest impact on the referendum will come if Thorpe, speaking for the black sovereignty movement, made common cause with the "No" committee. That would be a significant step and damaging for the prospects of the "Yes" vote. It would be a surprising alliance of disparate figures from the right and the left, but not unprecedented. Back in 1999 the single official "No" committee, appointed by the government, included both the right and the left. The former were status quo monarchists while the latter were direct election republicans advocating more substantial constitutional change.

This year will be different. The already announced "No" committee includes only right-wing opponents of the Voice from the Nationals and the broader community. It would be a coup for them if even a loose relationship with the black sovereignty movement emerged. The driver for the black sovereignty movement is their belief that not only is a Treaty a higher priority than the Voice but that a Voice, if successful, would impede movement towards sovereignty by enmeshing the Indigenous community in a colonial constitution.

This immediate implication will play out this year. There are others.

The first is that it changes the voting dynamics of the Senate on all matters. There is now another centre or left-leaning crossbench vote making four in all; the government will need two such votes to pass its legislation rather than just one plus the Greens. How that works out for the government is unpredictable. It just means that it is forced to extend its negotiation partners. The Voice legislation should get through with Jacqui Lambie Network's two votes plus David Pocock. Thorpe has also said she will vote with the Greens on climate action. Other issues may be more problematic.

The second consequence is that the Greens will be enormously disappointed. Victorian Green voters will too, and Thorpe's action, like Senator Cory Bernardi leaving the Liberals and Gee leaving the Nationals, raises again the question of whether it is unethical for MPs who leave their parties not to resign from the parliament immediately.

The Greens have suffered the loss of a senator and there will be further ramifications within the Victorian Greens including internal finger-pointing about Thorpe's preselection. But it may, however, have a silver lining for them in terms of party unity. They are now free to wholeheartedly support the Voice "Yes" case. Otherwise, they would have been walking on egg-shells for the whole year.

The actions of Thorpe pose many different tests. She herself will rise or fall as a political figure on her performance. The Greens have suffered a setback and must bounce back. The Albanese government must recalibrate its constant search for a majority for its legislation in the Senate.

The unity of all the political parties will be further tested. Are there any more Thorpe-like MPs waiting to leave their parties? The Liberals suffered Craig Kelly and George Christensen in the last Parliament and are still disrupted by Senators Gerard Rennick and Alex Antic. Liberal leader Peter Dutton faces a balancing act whether he decides "Yes" or "No" on the Voice.

Most of all Thorpe and those she wishes to represent are a test for the ability of Anthony Albanese to carry the community with him in this year's Voice to Parliament referendum.