Former US president Donald Trump directly addressed the charges against his family business, the Trump Organisation, during a political rally in Florida on Saturday night – and hinted at a possible defence.

Let's run through the background first, and then we'll get to Trump's comments.

On Thursday, prosecutors in New York unsealed an indictment against the Trump Organisation and its long-serving chief financial officer, Allen Weisselberg.

The charges relate to an alleged scheme, starting in 2005, to "compensate Weisselberg and other Trump Organisation executives in a manner that was off the books".

Prosecutors allege Weisselberg evaded taxes on $US1.76 million in income.

The 15 counts against the Trump Organisation and its CFO include scheme to defraud, conspiracy, grand larceny, criminal tax fraud and falsification of business records.

"The scheme was intended to allow certain employees to substantially understate their compensation from the Trump Organisation, so that they could and did pay federal, state and local taxes in amounts that were significantly less than the amounts that should have been paid," the indictment says.

It alleges Weisselberg received a number of perks from the company, such as rent on an apartment, two Mercedes-Benz cars, private school fees for two of his relatives, and cash bonuses, all in lieu of direct compensation.

The Trump Organisation allegedly kept internal spreadsheets tracking these perks, for which it did not withhold income tax. Meanwhile, Weisselberg did not report the indirect compensation in his tax filings.

Both Weisselberg and the Trump Organisation have pleaded not guilty. Trump himself has not been charged.

In a statement last week, the company accused prosecutors of using its CFO as "a pawn in a scorched earth attempt to harm the former president".

"This is not justice. This is politics," it said.

Trump struck much the same tone as he spoke to a crowd of his supporters in Sarasota, Florida last night, in just his second rally since leaving the White House. Though it must be said, he was a little more strident.

The former president said prosecutors' pursuit of his company was "fascist", "authoritarian" and "reminiscent of a communist dictatorship" targeting its political opponents.

Manhattan District Attorney Cyrus Vance is a Democrat. So is New York Attorney General Letitia James. The charges against the Trump Organisation and Weisselberg were approved by a grand jury of regular citizens.

The charges relate to an alleged scheme, starting in 2005, to "compensate Weisselberg and other Trump Organisation executives in a manner that was off the books". Photo / Getty Images

Trump said "every company" used "fringe benefits" and his was being singled out for political reasons.

"Never before has New York City and their prosecutors, or perhaps any prosecutors, criminally charged a company or a person for fringe benefits," he claimed.

"The people who talk about democracy are literally destroying it before our very eyes.

"The radical left continues to search for a crime and wreck lives, break laws, violate every principle of justice, fairness and liberty.

"It's really called prosecutorial misconduct. It's a terrible, terrible thing. There's no depth to which the radical left will not sink to stop our Make America Great Again movement."

Trump brought up President Joe Biden's son Hunter to suggest prosecutors "leave Democrats alone" but "mobilise every power of government to come after me".

Hunter Biden's tax affairs, stemming from his business dealings overseas, are currently being investigated by federal prosecutors in Delaware.

Most intriguingly, the former president specifically brought up several of the perks Weisselberg allegedly received off the books: the two cars, the New York apartment and the private school fees.

He appeared to admit that Weisselberg did not pay tax on them.

"They go after good, hardworking people for not paying taxes on a company car," he said.

"'You didn't pay tax on the car! Or a company apartment. You used an apartment because you need an apartment, because you have to travel too far where your house is. You didn't pay tax or education for your grandchildren.'

"I don't even know. Do you have to? Does anybody know the answer to that stuff? OK? But they indict people for that!"

Some observers, such as political reporter Andrew Feinberg and University of Alabama law professor Joyce Alene, characterised these quotes as a slip-up or an "admission".

But Trump may have been foreshadowing a strategy his company could use in its defence against the charges.

The idea is to argue that the defendants did not "wilfully" break the law.

"The fact that Trump and his company made these payments is likely indisputable," said legal analyst Renato Mariotti, a former federal prosecutor.

"What Trump is claiming is that they had no idea this was taxable income to Weisselberg, which is an attempt to argue that they didn't 'wilfully' fail to pay taxes. It's his attempt at a defence."

"This was an intentional legal strategy to combat the prior statements about how well he knows the tax code," said Daniel Goldman, a former assistant US attorney for the Southern District of New York.

"There is a heightened intent standard for tax crimes, and the District Attorney has to prove the defendant knew the law and wilfully broke it. This was his attempt to claim ignorance."

The prior statements Goldman mentioned are not hard to dig up.

"I know more about taxes than any human being that God ever created," Trump said in March of 2016, when he was a presidential candidate.

"I know our complex tax laws better than anyone who has ever run for president and am the only one who can fix them," he tweeted in October of that year.

These statements are consistent with Trump's longstanding habit of claiming to know more about many, many subjects than anyone else, but they could nevertheless undermine any effort to plead ignorance about New York's tax laws now.

Another obstacle for the defence is the set of records the Trump Organisation allegedly kept detailing its off-the-books compensation to Weisselberg.

University of Chicago law professor Daniel Hemel, writing for The Atlantic, said the Trump Organisation was "in big trouble". He disputed the former president's assertion that the case was merely about "fringe benefits".

"The Trump Organisation and Weisselberg aren't being charged with tripping over some hyper-technical provision on the margins of the tax system," said Hemel.

"They are being charged with blatantly violating basic tax law requirements, and bilking New York State and New York City out of hundreds of thousands of dollars along the way.

"If the Trump Organisation was keeping a separate set of books recording compensation that it didn't report to tax authorities, then this was no unintentional oversight.

"Yes, this is a politically tinged prosecution. But if the allegations in the indictment are true, it's also out-and-out tax fraud – conduct that is criminal beyond question.

"Being connected to a controversial political figure shouldn't send you to jail. It shouldn't get you off the hook either."