Barnaby Joyce hasn't quit the Nationals yet but he's got one foot out the door

Barnaby Joyce hasn't quit the Nationals. Yet. But the party's former leader and most high-profile member now has one foot out the door.

In declaring he won't be recontesting his lower house seat of New England and letting speculation run that he might jump ship for One Nation and return to the Senate, where he began his parliamentary career, Joyce is declaring he's had enough with the Nationals under David Littleproud.

In fact, the 58-year-old is letting the world know about his feelings towards the current leader.

The relationship, he says, "has unfortunately, like a sadness in some marriages, irreparably broken down".

This break-up is partly driven by policy, partly by personality.

The policy schism is squarely over net zero. This has become Joyce's overwhelming focus since the election.

As Nationals leader he may have done a deal with then-prime minister Scott Morrison to endorse the net zero by 2050 policy, but his view in the years since has hardened considerably against the climate target.

The Nationals are still officially reviewing their post-election position. Nearly everyone expects they will formally reject the target.

But Joyce is unwilling to wait.

Personality clash

On the personal front, the fall-out between Joyce and Littleproud dates back years.

The former leader has eyed the current leader with suspicion since he last lost the top job more than three years ago.

He blames Littleproud for sidelining him during the recent election campaign, dumping him from the frontbench, and placing him in the far corner of the backbench in parliament.

Joyce had been telling colleagues privately for some time this would likely be his last term as the member for New England.

The man who first made a name for himself as a political firebrand and floor-crosser was never going to sit quietly on the backbench.

His possible move to One Nation, however, poses a more dangerous threat to the Nationals than any backbench bomb-throwing.

For all his faults and controversies, including infamously being filmed sprawled on a Canberra footpath, Barnaby Joyce remains a politician with conservative cut-through.

Most notably it was Barnaby Joyce who began the move to bring down Labor's emissions trading scheme during the Gillard government years. Tony Abbott followed.

If Joyce were to jump to One Nation and possibly succeed Pauline Hanson as party leader in the Senate, this would deliver more than a blow to the Nationals. It would pose a threat.

When former Labor leader Mark Latham joined One Nation this was seen as a unique and somewhat strange political journey.

There was no mass movement from Labor supporters and branch members following him.

By contrast, Barnaby Joyce would be moving in the same direction as many Nationals voters and branch members already are. Every poll shows One Nation is on the rise and pulling votes from the Coalition.

Joyce's mission would be to bring more Nationals' supporters with him. That's why the Nationals should take this threat seriously.

Right now, Joyce insists he has made no decision on whether to make the move to One Nation.

Some of his Nationals colleagues suspect this is all part of an orchestrated campaign to string out the pain. In a divided party there are some who would quite happily see the back of him.

Others, however, know a One Nation party with Barnaby Joyce involved would pose dangers.

More broadly, Joyce's declaration he's had enough of being part of the Littleproud Nationals represents just the latest example of the turmoil and splintering on the conservative side of politics since the May election.

Liberals are divided over their direction, with talk of a possible split.

Now Nationals are once again being plunged into another round of instability.

Anthony Albanese has sometimes mused about building an even bigger majority than the 94 seats he won in May. 

It's not looking impossible right now.