WATCH: The Election Clash That Fueled Putin’s Ire Against Clinton

For months, reports of Russian interference in the 2016 presidential election have dominated the headlines. 

But the story traces back long before the race between Donald Trump and Hillary Clinton last year.

In fact, as the above scene from the new, two-part FRONTLINE documentary Putin’s Revenge explores, Vladimir Putin clashed with then-Secretary of State Clinton in 2011 over her condemnation of Russia’s parliamentary elections.

More than 100,000 Russians had taken to the streets demanding Putin’s ouster, after cellphone video surfaced showing alleged stuffing of ballot boxes and campaign officials filling out ballots. In comments that spread across the internet, Clinton weighed in, saying, “We do have serious concerns about the conduct of the election … The Russian people deserve the right to have their voices heard and their votes counted.”

The Kremlin saw Clinton’s comments as a message to protesters: “It was the first signal from the State Department [that] they’re really very serious in their attempts to interference in our internal political life,” Russian senator Andrei Klimov tells FRONTLINE.

And Putin himself believed Clinton was encouraging protests against him and threatening his hold on power. Russian journalist Yevgenia Albats tells FRONTLINE: “He said it was Secretary of State Hillary Clinton who provided funds and means to the Russian opposition and made them to get … on the streets.”

Clinton’s State Department said it was simply promoting democracy, but to Putin, Clinton had crossed the line.

“There’s no question he’s looking at revenge at Hillary Clinton,” Peter Baker of The New York Times tells FRONTLINE, adding, “He wanted to get her back.”

The protests around the Russian elections were just one of the turning points in the relationship between Putin and the U.S. that Putin’s Revenge explores. From filmmaker Michael Kirk and his team, the documentary draws on more than 50 in-depth interviews with heads of U.S. intelligence agencies, diplomats, Russian politicians, historians and journalists to tell the epic story of how Putin came to see the United States as an enemy.

Part one of the film, premiering tomorrow night, is a portrait of what makes Putin tick, his rise to power and how he came to see Clinton as an adversary. Part two, premiering Wednesday, Nov. 1, delves into Russian interference in the election, and the reaction under President Obama and now President Trump.

Against the backdrop of ongoing investigations into Russia’s role in the election, Putin’s Revenge is the must-watch, inside story of how we reached this point, what drives Putin, and what might happen next.

Watch part one of Putin’s Revenge tomorrow at 10 p.m. EST/9 p.m. CST on PBS stations (check local listings) and online. Part two premieres Wednesday, Nov. 1.