What we do and don't know about Russia's interference in the presidential election

On Thursday, the U.S. government formally retaliated against Russia for allegedly interfering with the U.S. presidential election. The Obama administration's actions represent a historically aggressive response to a cyberattack in America (or elsewhere).
SEE ALSO: President Obama sanctions Russia for hacking
The FBI and Department of Homeland Security issued a joint report formally accusing Russian intelligence operatives of gaining access to a “U.S. political party"—presumably the D