Despite what some Americans will tell you, the US constitution is not perfect.

When the US Founding Fathers gathered in Philadelphia in 1787 to write the constitution, most of the advice came from lawyers.

Perhaps a Hollywood screenwriter would have been better-placed to imagine scenarios for what could go wrong with the President of the United States.

The constitution didn't explain, for example, what the vice-president was for. The job was originally given to the person who came runner-up in the presidential election. Imagine Hillary Clinton as Mr Trump's VP.

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They sorted that out with the 12th Amendment in 1804 but neglected to decide what should happen if the president died.

Does the vice-president become the president or the acting president? Who becomes the new vice-president? Nobody knew.

Eight presidents died in office and everyone pretended rules had been written. But they hadn't.

The drama didn't stop there.

Who should be in charge if the president was in surgery or a coma? What about a stroke or if he lost the ability to distinguish reality from hallucination?

The 25th Amendment in 1967 provided solutions.

But the United States constitution still has not explained what happens if the president commits a crime and Congress decides against impeaching him.

Let's play this out to its logical conclusion...

Right now in the United States, that precise dilemma is before the courts as President Trump's lawyers try to prevent prosecutors from the State of New York obtaining the president's tax returns.

Their legal argument is that the person who serves as president, while in office, "enjoys absolute immunity from criminal process of any kind".

This has been rejected by the US District Court, but it has now been brought before the appeals court, where the President's lawyers made the same argument.

In the courtroom discussion, a famous Donald Trump quote was raised.

He said in 2016 that he could "shoot someone on [New York's] 5th Avenue and not lose any voters".

The Judge asked Trump's lawyer if, in his opinion, the President could be arrested by police if he shot someone on Fifth Avenue.

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Defence lawyer William Consovoy simply said "No".

As the appeals court considers ITS judgement, let's play this out to its logical conclusion.

So … what would happen if Donald Trump pulled out one of the guns he says he owns, walked out the front door of Trump Tower on Fifth Avenue, and shot someone at random.

The President would be surrounded by Secret Service agents, who can't arrest him as they follow his orders.

The FBI also couldn't arrest him.

The New York Police officer standing on the street corner, according to Trump's lawyer, also couldn't arrest him.

So he walks back into Trump Tower.

A prosecutor decides to charge him with murder and sends a subpoena demanding Trump appear before a Grand Jury.

The White House has argued in the past that the President can't be subpoenaed.

And if he's let off, what then? What's to stop him shooting someone on Sixth Avenue this time?"

According to the argument being put forward by the President's legal team, that would be the end of it, until he leaves office.

At which point, he'd be in a lot of trouble.

There's some suggestion that the President could potentially pardon himself for all crimes, though that has never been tested in a court.

The immunity question needs answers

Of course, that's all very far-fetched, but Mr Trump is facing a few more real-word legal problems and we're yet to see how they will be handled.

Last year the President was tied to the crimes related to payments, to a porn star and Playboy playmate, which his lawyer Michael Cohen is currently sitting in jail for.

Meanwhile, the Mueller Investigation has published a 200-page report describing in incredible detail a number of times Trump may have committed criminal obstruction of justice by attempting to impede the investigation or shut it down.

Now, as an impeachment inquiry is underway into the President's campaign to get the Ukrainian government to investigate the Democratic party, a simultaneous criminal probe is looking into some of his associates' activities related to the scheme.

While we may not know soon whether the President really "enjoys absolute immunity from criminal process of any kind", it's important that the US gets an answer.