OPINION: Revelations about US President Donald Trump's personal lawyer, Michael Cohen, become more intriguing – and horrifying – by the day.

Cohen is under criminal investigation by the Southern District of New York over his business dealings.

The Washington Post reported on Thursday (Friday NZ time): "Details that emerged this week reveal how Cohen quickly leveraged his role as Trump's personal attorney, developing a lucrative sideline as a consultant to companies eager for insight into how to navigate the new administration.

"The rapid flow of millions of dollars to Cohen shows the rush by corporations – unable to rely on the influence of Washington's traditional lobbying class in dealing with a new, populist outsider president – to lock in relationships with Trump's inner circle."

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Special Counsel Robert Mueller and the prosecutors and investigators from New York's Southern District have looked into whether a host of corporations collectively may have paid millions for something valuable in return.

("Both teams of investigators have scrutinised the intersection of Cohen's work and the president's interests - and how the activity flowed through Essential Consultants, a company Cohen formed in the fall of 2016 and used to pay hush money to an adult-film star who claimed she had an affair with Trump. Late last year, the special counsel sought information from two of the companies that hired Cohen, AT&T and Novartis, the companies said Wednesday.")

CAROLYN KASTER/AP In the best-case scenario for US President Donald Trump, investigators would find no evidence that he was aware of his lawyer's influence-peddling.

This alone raises a host of questions:

* Did Trump receive any of the money?

* Did Trump know of or approve this scheme?

* Did Cohen provide actual lobbying services?

* Did any of Cohen's clients get a tangible benefit (e.g. regulatory approval, legislation) in exchange for their money?

But it is the Russian connection that remains the most intriguing. Cohen's Essential Consultants provided the conduit for corporate monies, including Russian-linked money:

"Perhaps Essential Consultants' most notable contract was with Columbus Nova, a New York-based investment firm that said it paid Cohen $US500,000 [$NZ718,114] between January and August 2017," the Post reported.

"In a statement, Columbus Nova said it is owned and managed by Americans but acknowledged that it manages assets for a company controlled by the Russian billionaire Viktor Vekselberg.

"Columbus Nova said it paid Cohen to help it with investments such as real estate. It said Vekselberg had nothing to do with the decision to hire Cohen. Vekselberg attended Trump's inauguration with Andrew Intrater, his cousin and the head of Columbus Nova. A person familiar with their attendance at the inauguration said Cohen, Intrater and Vekselberg were seen together."

MARY ALTAFFER/AP Michael Cohen appears to have developed a lucrative sideline as a consultant to companies eager for insight into the Trump administration.

To be blunt: if Russian-linked funds went into Cohen's kitty and hush payments went out the other end, then we have the makings of a jaw-dropping plot that would likely be rejected by Hollywood moviemakers as too far-fetched.

In the best-case scenario for Trump, investigators would find no evidence that Trump was aware of any of the possible Cohen influence-peddling and no evidence that Russian money made its way to anyone with whom Trump allegedly had affairs; Cohen's work would not qualify as "lobbying" (for which he was not registered) and no quid pro quo would be uncovered.

Imagine now – even if all of that were true – how Republicans would react if Cohen were the lawyer for a Democratic president. This arrangement makes the Clinton Foundation's operation (lavish donations by those who later appeared to enjoy access to the Obama administration) look pristine.

If Cohen was getting rich off a Democratic president, Republicans would be hollering about a massive bribery scheme and drafting articles of impeachment.

However, there are far more dangerous scenarios for Trump and Cohen. Consider these possibilities:

MARK LENNIHAN/AP Michael Avenatti, Stormy Daniel's attorney, who released details of payments to Cohen on Wednesday.

Cohen and Trump communicated directly about any matter which Cohen was pursuing on behalf of paying clients.

Cohen is found to have performed illegal lobbying and therefore gets "flipped" to act as a cooperating witness on all matters relating to the president.

The list goes on.

The bottom line is that a set of facts entirely unrelated to the "collusion" issue may be enough to ensnare Cohen and/or the president. In that event, none of the smearing of the FBI, the firing of James Comey as FBI director, the plotting to fire Mueller or then-Deputy Attorney General Rod Rosenstein, or the hysteria over surveillance of Carter Page may have any relevance.

Trump and his retinue of media apologists might find that they have spent more than a year wasting their time blowing smoke in the wrong scandal. What fitting political karma that would be for months of lies, irresponsible accusations and assaults on democracy.