If you were paying attention to Vladimir Putin on Monday during his joint press conference with President Trump in Helsinki, you may have noticed that he suddenly brought up billionaire Bill Browder, the man who is pushing anti-Putin human rights legislation all over the world. Putin’s poker face cracked; he is clearly upset about Browder’s activities. It means that human rights sanctions are working.

Bizarrely, Putin proposed that, if Trump allowed Russian law enforcement to interview U.S. intelligence officials about Browder, he would allow special counsel Robert S. Mueller III’s team to interview the 12 Russian intelligence officers it just indicted for election interference — with Russian supervision, of course. The proposal is fundamentally unworkable for several reasons, but it shows what Putin’s priorities are.

Putin alleged that Browder and his associates evaded taxes on $1.5 billion earned in Russia and then transferred it to the United States — including a $400 million secret gift to the Hillary Clinton campaign — with the help of unnamed U.S. “intelligence officials.”

“So we have an interest in questioning them . . . That could be a first step, and we can also extend it,” Putin said, offering the trade under the auspices of 1999’s Mutual Legal Assistance Treaty between the United States and Russia. “Options abound.”

During a phone interview, Browder told me he was thrilled to be the subject of Putin’s proposal. It shows, Browder says, that Putin is annoyed by his legislation, the Magnitsky Act, which has been used to sanction Russian officials for human rights abuses each year since it was passed in 2012. The act is named after Browder’s accountant and lawyer, Sergei Magnitsky, who was tortured in a Russian prison and died there in 2009.

“This is an incredibly powerful tribute to the power of the Magnitsky Act. This shows I’ve found Putin’s Achilles’ heel, that he’s very rattled by it,” Browder said. “For a guy who’s supposed to be a former KGB spy, he’s got a terrible poker face.”

Despite Trump’s public and private disdain for human rights promotion, his administration has continued to issue sanctions under the Magnitsky Act, which was expanded to cover all countries in 2016, not just Russia. The State Department issued the most recent Magnitsky sanctions earlier this month.

The Russian government’s outrage over the law has been deep and consistent. Their initial response was to ban Americans from adopting Russian children. There has also been a fierce anti-Magnitsky lobbying campaign in Washington for years, led in part by Russian lawyer Natalia Veselnitskaya, who has close ties to Yuri Chaika, the prosecutor general of Russia.

Relief from Magnitsky sanctions was the ask that Veselnitskaya and her cohorts brought to the now-infamous June 2016 meeting at Trump Tower with Donald Trump Jr., Jared Kushner and Paul Manafort. As mentioned above, the Russians have artificially linked the adoption issue, which became part of the cover story about the meeting, to the Magnitsky legislation.

Putin claimed on Monday that Browder contributed heavily and secretly to Clinton’s campaign. That’s the same “dirt” Veselnitskaya was offering the Trump team. There is no public evidence that the assertion is true.

Veselnitskaya was working on the anti-Magnitsky case with Fusion GPS, the opposition research firm that commissioned the Christopher Steele dossier. But Fusion was working for an American law firm that had Veselnitskaya as a client. That work was unrelated to the dossier, though Trump defenders have sought to conflate the two.

The point is, from Putin down to Veselnitskaya, the Russian government and its proxies are working hard not only to get rid of the Magnitsky sanctions, but to prevent other countries from passing similar laws.

“That Putin keeps on bringing it up is a very powerful message to countries that haven’t passed the Magnitsky Act. It proves that it works,” Browder said.

Trump doesn’t see human rights advocacy as what it is — strong leverage that can be used to advance our interests and values at the same time. He has repeatedly said he doesn’t believe the United States should interfere in the internal matters of other countries. He often draws equivalences between free societies and repressive ones.

Perhaps if Trump realized human rights was the one thing that really gets Putin’s attention, he could use it to get the things he says he wants for America. By the way, the same tactic could also work for North Korea, Iran and China.

Russia convicted Browder in absentia for tax fraud in 2013, but Interpol has rejected Moscow’s requests for international arrest warrants because they view the conviction as politically motivated. Even if Trump wanted to hand him over, he couldn’t. Browder is a British citizen and lives in London.

“If Putin wants to have this conversation, he’d better have it with Theresa May, not Donald Trump,” Browder said.

Read more: