Clive Palmer has been labelled "the enemy" of Western Australia as his federal government-aided challenge to the state's tough border stance wrapped up in the Federal Court.
The Queensland billionaire argues WA's border closure is unconstitutional and damaging trade, while Premier Mark McGowan says it is necessary to protect citizens and is based on expert health advice.
The four-day hearing concluded on Friday, with WA's Solicitor-General Joshua Thomson saying in his closing submissions that no community transmission in the state since mid-April showed the closure was working.
Mr Thomson took aim at the quality of evidence by infectious diseases expert Peter Collignon, who was engaged by the Commonwealth and argued in favour of "targeted quarantine" for people from states with high levels of community transmission such as Victoria and NSW.
Mr Palmer's barrister Peter Dunning said the "attack" on the professor was completely without basis, noting WA had experienced community transmission that didn't lead to an outbreak amid high levels of contract tracing and compliance with COVID-19 rules.
Justice Darryl Rangiah reserved his findings and the matter will ultimately be decided by the High Court, with the judgment expected around October
Mr Palmer launched the action in May after he was denied an exemption to enter WA and Mr McGowan says the action shows he is only focused on himself.
"He is not focused on the health or the wellbeing of the people of this state," the premier said.
"Mr Palmer is an enemy of the state."
The businessman labelled Mr McGowan a liar, citing WA's chief health officer Andy Robertson's testimony that he had advised the state government that travel bubbles with low-risk jurisdictions could work, but had received no response.
"Now that's a lot different to the lies that Mark McGowan has told the people of Western Australia, that he's acted on advice of the chief medical officer," Mr Palmer said.
The United Australia Party leader said WA should keep its border closed to hotspots "but not lie to the Western Australian people about threats that don't exist".
"There is no threat to Western Australia certainly here in Queensland, in South Australia, the Northern Territory, the ACT and Tasmania."
Prime Minister Scott Morrison has repeatedly tipped WA will lose the case and Attorney-General Christian Porter suggests the same.
"There is a real risk that the High Court may find that the present zero compromise, total border closure is not constitutional," Mr Porter said.
He insisted the Commonwealth was not taking sides but said "we don't want to see an all or nothing approach" and urged the state government to consider a compromised arrangement ahead of the judgment.
But Mr McGowan dug in.
"It pains me that this is going on and I'm not enjoying it but we're not going to cave in," he said.
The Labor leader has repeatedly said the state government's legal advice was that it could not "pick and choose" jurisdictions it would allow travel from.