WASHINGTON — At the heart of Donald Trump Jr.’s unusual campaign-season meeting with a Russian lawyer was an obscure sanctions law that has infuriated the Kremlin.

The Magnitsky Act, passed by Congress in 2012, was a U.S. response to the dubious death of a different Russian lawyer named Sergei Magnitsky. He died in prison after exposing a tax fraud scheme. The law has allowed the U.S. to impose sanctions on Russians deemed to be human rights violators.

The law also led Moscow to respond by banning Americans from adopting Russian children, devastating some would-be U.S. parents.

After changing his initial story, President Donald Trump’s eldest son, Donald Trump Jr., now says he met attorney Natalia Veselnitskaya last year to hear damaging information she said she had on Hillary Clinton. Trump Jr. said it quickly became clear Veselnitskaya had nothing valuable to offer on Clinton and the discussion turned to the Magnitsky Act and adoption ban.

“The claims of potentially helpful information were a pretext for the meeting,” Trump Jr. said in a statement.

A look at the sanctions law Trump Jr. and Veselnitskaya supposedly discussed:

Q: What prompted the law?

A: Sergei Magnitsky was a Russian lawyer hired by Hermitage Capital, a London-based hedge fund. Magnitsky accused Russian officials of a $230 million tax fraud scheme involving tax rebates. He was charged by Russian officials with tax evasion and put in prison, where he died at 37.

An official Russian probe blamed a heart attack. But Russia’s presidential council on human rights concluded he’d been beaten and denied medical treatment. A prison doctor, the only official charged in the case, was acquitted.

Magnitsky’s death drew widespread criticism from human rights activists, triggering efforts to punish Russian officials associated with abuses of human rights.

Q: What does the law do?

A: The law initially allowed U.S. sanctions on Russian officials believed to be complicit in the Magnitsky case. It expanded in 2016 to include human rights abusers anywhere. Several dozen people are now subject to U.S. sanctions under the law.

Americans are prohibited from doing any business with these individuals. Any assets they may have in the United States are frozen.

Q: How did Moscow respond?

A: In December 2012, shortly after President Barack Obama signed the Magnitsky Act, Russian President Vladimir Putin signed a law banning American citizens from adopting Russian children.

Russia justified its adoption ban by pointing to cases of mistreatment of Russian children in the U.S., including the death of a 7-year-old who authorities said was beaten and starved to death, and another whose adoptive family put their unruly child on a flight back to Moscow, raising accusations of abandonment.

Yet it was widely viewed as retaliation for the Magnitsky law. The ban abruptly halted plans for 50 children to join new families in the U.S. and led to worsening U.S.-Russian relations.

Q: What’s the connection to Trump Jr.’s meeting?

A: Veselnitskaya, the lawyer who Trump Jr. met with, opposes the Magnistky sanctions. She has represented Denis Katsyv, the son of a top executive in state-owned Russian Railways. He was charged in the U.S. with money laundering after investigators suspected his company bought ritzy New York real estate using proceeds from the $230 million tax fraud scheme that Magnitsky exposed.

Trump Jr. said that after initially discussing Clinton, Veselnitskaya “changed subjects” to the adoption ban and the Magnitsky Act. He said he interrupted her to say that since his father wasn’t yet an elected official, the conversation should wait until “if and when he held public office.”