A congressional committee probing Russian interference in the 2016 U.S. election could broaden its investigation to look at Reddit and 4Chan as potential tools of clandestine activity, according to a congressional aide.

The Hill reported Wednesday that Sen. Mark Warner, the ranking Democrat on the Senate Intelligence Committee, wants to look at the loosely controlled internet message boards, which became a hub for the so-called alt-right during the election.

The investigation is already probing Facebook and Twitter over claims of Russian meddling.

The controversial TheDonald subreddit, which launched the same day Trump confirmed his candidacy, will be of particular interest.

It has been described as a “safe-harbor” for racists, white-nationalists, and white supremacists to express their views and spread conspiracy theories, Islamophobia, and anti-Semitism.

According to the Economist, “few corners of the internet are fouler.”

The subreddit has gained notoriety for promoting conspiracy theories, including Pizzagate and the Seth Rich murder. The infamous video of Trump body-slamming CNN first appeared there.

The notorious 4Chan message board, where anonymous users fear few restrictions, already has a link to Trump. While still a candidate, the businessman tweeted an image of Pepe the Frog, a meme that originated on the 4Chan site and has strong links to far-right groups, anti-Semites, and racists.

Users of 4Chan started a discussion Wednesday on the possibility of their actions becoming the focus of a Congressional investigation.