When mass protests against Russian President Vladimir Putin erupted in Moscow in December 2011, Putin made clear who he thought was really behind them: Secretary of State Hillary Clinton.

With the protesters accusing Putin of having rigged recent elections, the Russian leader pointed an angry finger at Clinton, who had issued a statement sharply critical of the voting results. “She said they were dishonest and unfair,” Putin fumed in public remarks, saying that Clinton gave “a signal” to demonstrators working “with the support of the U.S. State Department” to undermine his power. “We need to safeguard ourselves from this interference in our internal affairs,” Putin declared.

Five years later, Putin may be seeking revenge against Clinton. At least that’s the implication of the view among some cyber-security experts that Russia was behind the recent hack of the Democratic National Committee’s email server, which has sowed confusion and dissent at the Democratic convention and undercut Clinton’s goal of party unity.

While Donald Trump’s budding bromance with Vladimir Putin is well known— the two men have exchanged admiring words about one another, and called for improved relations between Washington and Moscow — Putin’s hostility towards Clinton draws less attention.

Former U.S. officials who worked on Russia policy with Clinton say that Putin was personally stung by Clinton’s December 2011 condemnation of Russia’s parliamentary elections, and had his anger communicated directly to President Barack Obama. They say Putin and his advisers are also keenly aware that, even as she executed Obama’s “reset” policy with Russia, Clinton took a harder line toward Moscow than others in the administration. And they say Putin sees Clinton as a forceful proponent of “regime change” policies that the Russian leader considers a grave threat to his own survival.

While experts debate whether Putin would actually try to meddle in a U.S. election, there is consensus on the idea that Clinton is unloved within the Kremlin.

“He was very upset [with Clinton] and continued to be for the rest of the time that I was in government,” said Michael McFaul, who served as the top Russia official in Obama’s national security council from 2009 to December 2011 and then was U.S. ambassador to Moscow until early 2014. “One could speculate that this is his moment for payback.”

The notion of payback remains speculation. Some experts are unconvinced that Putin’s government engineered the DNC email hack or that it was meant to influence the election in Trump’s favor as opposed to embarrassing DNC officials for any number of reasons.

But the Clinton campaign has embraced the theory, with campaign manager Robby Mook seeming to endorse the notion of Russian involvement on CNN Sunday. Clinton aides have been gratified to see the story leap onto television, which had previously given little coverage to Trump’s views about Russia, and noted that even Fox News commentator Charles Krauthammer on Sunday called the allegation of Russian meddling “troubling” and “plausible.”

And while Clintonites realize that few Americans typically pay close attention to the state of U.S.-Russia relations, there are two important caveats. One is the presence of large Polish, Ukrainian and other eastern European populations in Rust Belt states like Pennsylvania, Ohio and Wisconsin, where the Clinton campaign plans to flag stories about Trump and Putin for ethnic media outlets. The other is that voters of all stripes will surely pay attention to serious talk of foreign influence in the election.

While experts debate whether Putin would actually try to meddle in a U.S. election, there is consensus on the idea that Clinton is unloved within the Kremlin. “I think there is good and credible evidence that there is no love lost in Moscow for Mrs. Clinton,” said Eugene Rumer, a former national intelligence officer for Russia and Eurasia at the National Intelligence Council now at the Carnegie Endowment for International Peace.

Clinton has never concealed her own disdain for Putin. As a senator in 2008 she joked about George W. Bush’s famous line that he’d gotten a sense of Putin’s “soul,” cracking that because Putin was a KGB agent, “by definition he doesn’t have a soul.”

On arrival in the Obama administration in 2009, at a moment of U.S.-Russian tensions over Putin’s 2008 invasion of the Republic of Georgia, Clinton was tasked with implementing Obama’s “reset” of relations with Moscow, an attempt to collaborate on areas of common interest even while acknowledging unresolved differences on a range of issues. Though skeptical of the effort, Clinton felt that Dmitry Medvedev, a former prime minister who had swapped jobs with Putin to become president, might be easier to deal with than Putin.

“Clinton was a more skeptical voice on the reset,” McFaul says. “She was tougher on the Russians. She pushed back. She was a difficult interlocutor with both [foreign minister Sergei] Lavrov and Putin — and I say that as a compliment.”

The reset effort was troubled from the very start: Clinton arrived with a novelty button for a press conference with Lavrov. It was supposed to say “reset,” but instead said “overload” — which Lavrov didn’t fail to mention. Clinton became the butt of Russian jokes over this typo. Yet the reset had its successes, including a NATO transit point on Russian soil for troops headed to Afghanistan and a new nuclear arms reduction treaty.

Behind the scenes, however, Clinton and Putin — who, it soon became clear, was still the real power in the Kremlin — had an uneasy dance. In March 2010, when Clinton visited Russia, Putin summoned her to his luxurious residence outside Moscow. Knowing her fondness for wildlife elephants, in particular — Putin invited Clinton to a basement trophy room filled with mounted animal heads. (A Clinton aide later described the gesture, though well meaning, as having a Bond villain feel.) Yet when the two emerged for a photo-op, Putin launched into a public scolding of Clinton. The slouching Russian rattled off a list of complaints, from a decline in U.S.-Russia trade in to the impact sanctions against Iran and North Korea were having on Russian companies.

Putin has repeatedly criticized the U.S. for “regime change” policies that have toppled authoritarians in other countries, including Iraq and Libya.

But Clinton knew how to play tough with the Russian officials, some of whom referred to her with both derision and respect as “a lady with balls.” When McFaul arrived in Moscow in January 2012, he faced harassment, including the reporter with a Kremlin-controlled TV channel who followed him everywhere and the Russian secret services who followed his children to school.

One day, Clinton called an exasperated McFaul at the ambassador’s residence in Moscow to express her anger at the Russian violation of diplomatic protocol. McFaul was stunned that Clinton had called on an unsecure line, especially when the two had plans to meet soon anyway. “Oh, I want them to know that I know,” Clinton said, in McFaul’s recollection.

In September 2012, Clinton was to meet with Lavrov on the sidelines of the APEC summit in Vladivostok, Russia. Lavrov, a sophisticated member of the Soviet foreign policy aristocracy, took great pleasure in being gentlemanly toward Clinton. He personally picked out the flowers for her hotel room in Vladivostok. But when they met, Lavrov slammed her with some unexpected news: Russia was kicking out USAID and gave the Secretary of State 30 days to pack them up and move them out. Stunned, Clinton stood up and walked out. According to people with knowledge of the meeting, Lavrov tried to get her to stay and talk, but Clinton wasn’t having any of it. She dropped her notes and said he could read those if he wanted to talk, and walked out.

But nothing angered Putin as much as Clinton’s statement about Russia’s December 2011 parliamentary elections, which produced widespread allegations of fraud and vote-rigging on behalf of Putin allies. At a conference in Lithuania, Clinton issued a biting statement saying that the Russian people “deserve to have their voices heard and their votes counted, and that means they deserve fair, free transparent elections and leaders who are accountable to them.” Some Obama officials felt the provocative statement went too far.

It certainly provoked Putin, who soon accused his opponents of organizing with State Department money. One former State Department official who worked on Russia issues under Clinton suggests that Putin’s outrage over that statement might have been manufactured, a classic effort by a strongman to tarnish his domestic opposition as foreign puppets. McFaul says he is confident that Putin was genuinely angry.

Since leaving government, Clinton has had almost exclusively tough words for Putin, especially following Russia’s 2014 annexation of Crimea.

Whether Putin genuinely believed that Clinton was plotting his overthrow is another question. But he has repeatedly criticized the U.S. for “regime change” policies that have toppled authoritarians in other countries, including Iraq and Libya that Clinton supported. In the latter case, Putin was furious when a 2011 U.S. and European military operation billed as humanitarian—and advocated by Clinton—evolved into a de facto campaign against dictator Muammar Qadhafi.

Putin reportedly obsessed over Qaddafi’s violent death in Kremlin meetings. The graphic video of the Libya ruler’s bloodied body being dragged by a mob is often replayed on Russian television, along with Clinton’s wisecrack about the executed strongman: “We came, we saw, he died.”

Since leaving government, Clinton has had almost exclusively tough words for Putin, especially following Russia’s 2014 annexation of Crimea. At a March 2014 fundraiser, Clinton compared Putin’s action “to what Hitler did back in the ’30s.”
But few would have guessed that Clinton herself might wind up wondering whether she herself had become a target of Putin’s aggression.

“I think they expect her to win,” said one diplomat with extensive Russia experience, who believes the Kremlin directed the email hack. “But they’re sending her a message that they are a power to be reckoned with and can mess with her at will, so she had better take them seriously.”