As then-candidate Donald Trump pursued a deal for a Trump Tower in Moscow in 2015, his associates floated the idea of offering a penthouse in it to Vladimir Putin as a marketing ploy, according to a BuzzFeed report in late November. That might sound like a bribe, to some observers, even if they never acted on it.

It's just one of many kickback-type situations swirling around Trump and others involved in his campaign. And special counsel Robert Mueller's team has the right expertise to handle these matters as the Russia investigation unfolds.

One of Mueller's senior prosecutors, Andrew Weissmann, was the former chief of the DOJ’s Criminal Fraud division, where he decided anti-bribery policy at a very high level. Another member of his legal team, Greg Andres, oversaw the DOJ’s foreign bribery program.

“[Mueller] brought in expertise in the way these deals are arranged to look very innocuous,” David Montero, author of "Kickback: Exposing the Global Corporate Bribery Network_,"_ told VICE News, “Because the thing about bribery deals is they're always arranged to look very legitimate.”

Prosecution of bribery cases has been ramping up since 1997, when members of the OECD agreed to pass laws that criminalized bribery. They were following the U.S., which had signed the Foreign Corrupt Practices Act, or FCPA, in 1977 to outlaw U.S. corporations from bribing foreign officials. “It was a moment of reckoning that gave birth to this law,” said Montero. “These kickbacks were not only affecting our image; they were potentially destabilizing our allies and feeding into the hands of some of our enemies.

Despite its illegality, bribery is still a huge problem — especially in real estate and construction. Corporations around the world pay somewhere between $400 billion and $1 trillion a year in bribes. So it wouldn’t be a surprise if Trump’s relationship with Russia was built around the exchange of favors, legal or not.