According to Washington Post, US Cyber Command attacked one of Russia's online Troll operations centers on the day of the Congressional election. The offensive operation took place on the day the midterm elections took place and a pre-emptive strike to prevent a probable invasion of Russia.
The report notes that the main purpose of the offensive operation is an Internet research agency; a privately owned corporation affiliated with the Kremlin, and is often used to carry out a series of fake publishing operations.
The Washington Post, quoting a source that was aware of the operation, argued that the Research Agency was completely interrupted on the election day, as the staff of the agency complained of interrupting Internet access.
This attempt is one of the most aggressive US CYBERCOM operations that has been announced so far and poses many questions about the legitimacy of such operations.
Theoretically, the infrastructural attacks against an entity of a foreign government can result in considerable diplomatic responses and even be considered "action of war". However, in practice, such efforts [cyber-attacks] are rarely officially attributed to a specific person, group or government, and their political feedback is generally low.
It should be noted that last June, the Pentagon added to US military cyber command powers to cover more aggressive operations, which is in complete contradiction with its former mission and defense. Interestingly, these changes were applied just days before the invasion on the day of the 2018 congressional election.