Attorney General Jeff Sessions is recusing himself from the politically explosive investigations into Russia’s interference with the presidential election because of revelations that he’d personally met with Russian ambassador to the US Sergey Kislyak — and then failed, under oath, to acknowledge those meetings during his Senate confirmation hearings.

If Kislyak’s name sounds vaguely familiar, it’s because the veteran diplomat was also at the center of the earlier Russia scandal that led to the resignation of former National Security Adviser Michael Flynn. Flynn left the White House in February after reports emerged that he had lied to Vice President Mike Pence about discussing sanctions on Russia with Kislyak during a phone conversation in December.

But it turns out that wasn’t the only interaction between Flynn and Kislyak. On Thursday afternoon, the White House — potentially trying to get ahead of more damaging revelations — said that Kislyak and Flynn also held a previously undisclosed meeting in December. Also present at the meeting with Kislyak: Jared Kushner, Trump’s son-in-law and consigliere.

That makes Kislyak the common thread between the two firestorms of controversy surrounding the White House’s unusual relationship with Russia. Flynn and Sessions both failed to be honest with the public about their interactions with him, and those lies have exacted an enormous toll on their reputation: Flynn resigned, and the Democratic leadership is now calling for Sessions to do so as well. On Thursday, Sessions, bowing to mounting GOP pressure, announced that he was recusing himself from the escalating FBI probe into Moscow’s meddling in the 2016 presidential campaign.

Flynn and Sessions have taken a hit because they attempted to cover up their communication with Russia, not because of the communication itself. But the very fact that the officials felt the need to try to cover their tracks adds to the towering stack of questions surrounding the Trump administration’s ties to Russia. And it calls into question what the new president hopes to gain from his seeming willingness to make concessions to Moscow.

Russian diplomats around the world have traditionally had close ties to the country’s intelligence services, and there are claims in the intelligence community that Kislyak is a spy. There’s no proof, however. And nothing that has emerged in leaks about the ongoing FBI probes into the envoy’s dealings with the Trump administration suggests agents are looking into whether or not he’s a spy.

The fact that Kislyak was the point of contact in both situations is not in and of itself controversial or surprising. He is the Kremlin’s top diplomat to the US, and it makes sense that he’d be in contact with a presidential campaign and then an incoming administration looking to dramatically change Washington’s relationship with Russia.

Still, understanding Kislyak’s history and reputation is critical to getting a clearer sense of how he operates, what his goals are, and why senior US officials should have been more cautious in their dealings with him.

Kislyak surfaces again and again in Trump’s march to the White House

During his confirmation hearing, Sen. Al Franken asked Sessions, then a senator, what he’d do if any evidence emerged that Trump’s campaign communicated with Russian government.

“I’m not aware of any of those activities,” he responded. “I have been called a surrogate at a time or two in that campaign and I did not have communications with the Russians.”

Here’s the money shot of Sessions lying to Franken (if you believe the WaPo report). pic.twitter.com/0vK12oMed1 — Jamie O'Grady (@JamieOGrady) March 2, 2017

Except, as the Washington Post reported, Sessions, while a senior member of Trump’s campaign, did meet with Russians — twice. And both times it was with Kislyak.

Sessions officially joined Trump’s campaign in February, introduced Trump at rallies, and served as one of his top advisers on his signature issues of immigration and foreign policy. In July, he went to a Heritage Foundation event on the sidelines of the Republican National Convention, where 50 ambassadors were also in attendance. After the event, Sessions was approached by a number of those ambassadors whom he spoke to individually. Kislyak was one of them, according to the Washington Posts’ Justice Department source. According to a USA Today report that broke on Thursday, two other Trump campaign officials who advised on national security issues, J.D. Gordon and Carter Page, also spoke to Kislyak at that gathering.

Two months later, in September, Sessions had a one-on-one meeting with Kislyak in his senate office. This meeting occurred during the time of Russia’s cyberhacking campaign designed to interfere with the election and tip it in favor of Trump.

Sessions’s defense has been that he was answering the confirmation hearing question with regard to his involvement in the campaign, not his general responsibilities as a senator, which involves talking with foreign diplomats. Sessions's spokesperson Sarah Isgur Flores said Sessions "was asked during the hearing about communications between Russia and the Trump campaign — not about meetings he took as a senator and a member of the Armed Services Committee."

We don’t have any idea of what Kislyak discussed with Sessions in either exchange, but considering that he was part of Trump’s campaign and Trump was signaling interest in warming ties with Russian President Vladimir Putin, it certainly seems like the future of US-Russian relations could’ve come up.

Kislyak was also at the center of the Flynn flap. On the day in December that former President Barack Obama announced he was imposing sanctions on Russia and expelling Russian diplomats in response to its cyberhacks, Flynn made a series of calls to Kislyak. When reports of one of the calls emerged in January, Flynn originally said he had not discussed US sanctions on Russia during the call, which may have been a violation of the Logan Act, which prohibits people outside the executive branch from making foreign policy on behalf of the US administration. But after a damning Washington Post report cited several intelligence officials that said he did — and suggested Flynn had personally lied to Pence about it — the national security adviser ended up resigning.

Some sources told the Washington Post that Flynn suggested to Kislyak that Moscow shouldn’t overreact to Obama’s new sanctions, as Trump was likely to review them, and possibly lift them, when he took office. (US Intelligence agencies regularly surveil phone conversations with foreign intelligence targets.)

The next day, Putin surprised observers inside and outside the US government by failing to stick to his normal pattern of reacting harshly to US sanctions or diplomatic attacks. It seems reasonable to deduce that Putin was holding back in part at Kislyak’s recommendation — a proposal likely drawing on the Russian envoy’s conversations with Flynn. Kislyak, even critics agree, is very good at his job.

Sergey Kislyak is skilled at pushing for Moscow’s interests

Kislyak, who is 66 years old, has spent his entire career in the Russian foreign service. He had his first extended stint in the US between 1985 and 1989, during then-President Mikhail Gorbachev’s attempt to reform the Soviet Union before it collapsed a short time later.

Since then, he’s had several other high-profile gigs in the ministry of foreign affairs. Currently he’s on his third extended stay in the US, which began when he was appointed ambassador to the US in 2008.

Kislyak isn’t the most high-profile ambassador — he doesn’t tend to go on media blitzes to push Russian interests in times of crisis — but he’s widely respected in Washington and considered skilled at what he does.

Matthew Rojansky, director of the Kennan Institute at the Woodrow Wilson Center, has interacted with Kislyak and says his experience and social skills have made him an effective emissary for Moscow in Washington.

“He can be charming and entertaining and really understands the important role of personal respect in diplomacy,” Rojansky says. “So generally a very capable guy, very professional and by the book. “

Kislyak is especially adept at discussing arms control and security issues. “He has real technical mastery of the details from his time as a nuclear negotiator,” Rojansky says.

Evelyn Farkas, a former deputy assistant secretary of defense for Russia, Ukraine, and Eurasia, said Kislyak “has a reputation as a professional diplomat who can be blunt, firm, and charming in the same conversation.”

Kislyak is known more as a technocrat than an ideologue, disciplined in taking the line that Moscow wants without too much zeal. Since US-Russian relations have deteriorated dramatically in recent years, especially after Russia’s annexation of Ukrainian territory in 2014, that’s often meant taking a hard line on many issues of mutual concern for the US and Russia.

There is a certain degree of mystery that swirls around Kislyak. CNN reports that current and former intelligence officials say that Kislyak is not just a shrewd diplomat, but also a high-level spy — and an effective recruiter of spies as well. That is in fact apparently part of why intelligence officials were so unnerved by Flynn’s talks with him. Russia denies this and the Russia experts I spoke to said they were unaware of this reputation.

Kislyak is not considered a member of Putin’s inner circle, but Rojansky estimates that “they interact personally.”

So what should we take away from all this? Without knowing the substance of Kislyak’s interactions with Flynn or Sessions or Kushner, it’s impossible to know what was said, what was implied, or what each side took away from the talks. But it’s safe to assume that the skilled Russian envoy may have gotten the better of neophytes with no experience in high-level diplomacy or expert knowledge of Russia.