Australia's deputy prime minister, Barnaby Joyce, was briefly evicted from office last year over a dual citizenship eligibility saga. Now, two months after Mr Joyce's return, a fresh scandal threatens to oust him again.

Mr Joyce is facing damaging political questions arising from his relationship - which began as an extramarital affair - with a staffer who once served in his office.

The scandal has dominated national attention since a photo of the ex-staffer, Vikki Campion, was featured on the front page of Sydney's Daily Telegraph last Wednesday, showing her pregnant with Mr Joyce's child.

Immediately it sparked debate about justifications for publishing the image. In Australia, the private lives of politicians are largely kept out of the public eye.

But arguments for the story's public interest quickly emerged.

Why is Mr Joyce in political trouble?

At first, Mr Joyce, leader of junior coalition party the Nationals, was accused of hypocrisy. One criticism focused on his reasons for opposing same-sex marriage before it was legalised by Australia.

During that debate, the conservative politician argued the previous marriage definition had "stood the test of time". However, he also acknowledged that many such unions failed.

"I'll acknowledge that I'm currently separated, so that's on the record," he told parliament in December.

He also faced criticism that he may have disingenuously represented his family life to voters during his campaign to win a by-election last year. Had he lost, Prime Minister Malcolm Turnbull would no longer have a parliamentary majority.

Other revelations, including that Mr Joyce was now living rent-free in a businessman's property, have also drawn criticism; he had recently encouraged Australians to move away from expensive cities.

But the greatest worry for Mr Joyce is the intense discussion over whether he has broken any rules.

That debate concerns how Ms Campion, a former journalist turned media adviser, came to take up two jobs with his senior colleagues last year.

Ms Campion left Mr Joyce's office last April to take up a post with Minister for Resources and Northern Australia Matthew Canavan.

When Mr Canavan was also caught up in the dual citizenship saga, Ms Campion moved briefly back to Mr Joyce's office, then landed a new job with Nationals MP Damian Drum.

Political opponents have questioned whether the unadvertised positions, reported by local media to be well paid, may be evidence that Mr Joyce breached a ministerial code of conduct.

Under the code, partners and relatives of ministers cannot be given jobs with other ministers or executive officials without Mr Turnbull's permission - which was not sought for Ms Campion.

Both Mr Joyce and Mr Turnbull have denied that Ms Campion was the deputy prime minister's partner at the time of the appointments. The government has said she was "eminently qualified".

"It is without a shadow of a doubt that Vikki Campion is my partner now," Mr Joyce said on Tuesday.

"But when she worked in my office, she was not my partner. When she worked in Matt Canavan's office, she was not my partner. And Damian Drum was not a minister."

In a short press briefing, Mr Joyce also apologised to his estranged wife Natalie Joyce, their four daughters, and Ms Campion, for enduring a "searing personal experience".

Last week, Mrs Joyce described the situation as devastating: "For my girls, who are affected by the family breakdown, and for me as a wife of 24 years, who placed my own career on hold to support Barnaby through his political life."

She said in a statement that she believed the affair had been "going on for many months and started when [Ms Campion] was a paid employee".

Can he continue?

Mr Joyce has established prominent profile, and popularity among constituents, during a parliamentary career that began in 2004.

As agriculture minister in 2015, Mr Joyce famously gave US actors Johnny Depp and Amber Heard an ultimatum to remove their dogs, Pistol and Boo, from Australia, over a breach of quarantine regulations.

Mr Joyce explained that Australia had "strict biosecurity requirements for good reasons". Later, when the dogs were removed, he tweeted just two words: "Dogs gone".

The unusual saga, like the tweet, in part reflected Mr Joyce's no-nonsense, straight-talking style - traits for which he is well known. But it also promoted effectively the Nationals' core focus on regional issues.

Former Prime Minister Tony Abbott once described Mr Joyce as the nation's best "retail politician".

However, his standing has been diminished in the last week, according to public statements by prominent former Nationals.

Mr Joyce's current colleagues appear split over his future. In the end, it may be up to them to decide.