If you're not familiar with the Magnitsky Act, a 2012 U.S. law, here is the most important thing to understand: Russian President Vladimir Putin and everyone in his orbit hates it.

"A purely political, unfriendly act," Putin called it at the time, and he has been railing against it ever since.

Congress wanted to punish Russian human rights abusers by barring them from entering the U.S. This followed the 2009 death of Sergei Magnitsky, a Russian lawyer who died at age 37 in a Moscow prison where he was held — and allegedly beaten — after accusing Russian officials of massive tax fraud.

The law symbolized the deteriorating relations between the U.S. and Russia. Days after Congress passed it, the Russian parliament responded by banning American citizens from adopting Russian orphans.

In a bizarre 2013 trial, a Russian court went even further, convicting Magnitsky of tax fraud — four years after he died.

The Magnitsky Act re-emerged as a front-burner topic this week in connection with the investigations surrounding President Trump's campaign and possible links to Russian meddling in last year's presidential race.

Russia has lobbied hard for repeal of the act. That's what Russian lawyer Natalia Veselnitskaya said she was doing when she met with Donald Trump Jr. in June 2016 at Trump Tower in New York.

News broke Friday that she was accompanied at that meeting by Russian-American Rinat Akhmetshin. He is known as a skilled political operator who has worked in both the former Soviet Union and the United States on behalf of his clients, according to a U.S. journalist who has known him for two decades.

Akhmetshin has also spoken freely about his past in Soviet military intelligence, according to the journalist, Steve Levine, who works for in Washington.

However, in remarks to The Associated Press, Akhmetshin said he served in a military unit that was part of counterintelligence but was not trained as a spy.

Levine first encountered Akhmetshin in Kazakhstan. There, in 1998, he provided Levine with confidential banking and legal documents pointing to financial corruption by the country's president.

"His signature is to be able to drill very, very deeply in the former Soviet Union, in a very knowing way," Levine said. "Here in Washington, he's this very unusual character, who may be the most skilled lobbyist I've met."

Akhmetshin is, he added, "someone who can ingratiate himself with members of Congress and their staffs, power figures here, and make things happen."

Levine said they've been in touch periodically over the years, including in brief email exchanges in recent days as Akhmetshin's name began to surface in media reports.

Akhmetshin, who has become a U.S. citizen, has aggressively lobbied against the Magnitsky Act. Just a few days after his meeting with Trump Jr. in New York last year, Akhmetshin was in Washington to promote a movie called The Magnitsky Act — Behind the Scenes.

The film was shown at the Newseum in Washington on June 13, 2016. It offers the Russian government's version of events and claims that Magnitsky was not mistreated by Russian authorities.

Trump Jr. has also said that — to his disappointment — last year's meeting with the Russians focused on the Magnitsky Act. Trump Jr. was told in advance the meeting would produce critical material on Democratic presidential candidate Hillary Clinton. When the topic turned out to be the U.S. law, he considered it a waste of time.

Analysts have offered many theories on why Russia wanted to meddle in the U.S. presidential election: to undermine the credibility of the U.S. vote or to harm Hillary Clinton, whom Putin blamed for the protests leading up the Russian presidential election in 2012.

Rarely mentioned is the Magnitsky Act, a relatively obscure matter inside the U.S. but a major frustration for Russia's leadership.

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