Donald Trump first met Michael Cohen 13 years ago. He was on a residents' committee at a Trump property.

Donald Trump said Cohen did him a favour while he was on that committee. He said he was impressed by him and decided to hire him as his lawyer.

It was decision that both men now say they regret. Cohen became much more than Donald Trump’s lawyer.  He was his fixer and his right-hand man.

On Wednesday, Cohen was sentenced to three years in prison. He had pleaded guilty to campaign finance violations and had admitted being involved in the payment of hush money to two women who claimed they had had affairs with Donald Trump.

Cohen had also pleaded guilty to tax and bank fraud charges and had admitted lying to Congress about a Trump property deal in Russia.

At his sentencing hearing, Cohen pleaded for leniency and said Donald Trump had caused him to "follow a path of darkness rather than light".

He claimed his "weakness was a blind loyalty to Donald Trump" and that he felt it was his duty to cover up Mr Trump’s "dirty deeds".

In a follow-up interview with ABC News, Cohen said Mr Trump had instructed him to make hush money payments, adding that the then Republican candidate for the US presidency knew it was wrong and that it was done to help his campaign.

This is potentially a big problem for President Trump.

The Robert Mueller Russia investigation has resulted in arrests, plea deals, jail sentences and guilty pleas but it’s not yet clear how much evidence there is of Mr Trump’s direct involvement in the crimes being investigated.

In a misspelt tweet, Mr Trump recently claimed there was no "smocking gun" but the campaign finance violation charges are different.

Here we have Cohen and the prosecution claiming that Mr Trump directed his lawyer to break the law by making hush money payments to women.

Mr Trump has dismissed Cohen as a weak man and a liar who is making up stories to get a shorter sentence.

He recently tweeted; "He was a lawyer and he is supposed to know the law. It is called advice of counsel."

Mr Trump’s current lawyer Rudy Giuliani first claimed that the payments weren’t campaign finance violations because they were "personal". His argument has now evolved into claims that campaign finance violations aren’t a big deal.

Mr Giuliani - a former mayor of New York City - told The Daily Beast that "Nobody got killed, nobody got robbed," adding, "this was not a big crime."

However campaign finance violations are crimes and, what’s more, in this instance they could well have helped a candidate win a presidential election. Surely a matter to be considered a "big deal".

Cohen once claimed he’d take a bullet for Mr Trump, but now many are wondering if he will be the "smocking gun" that brings down a president.