Russian bots’ support for the Trump agenda is now a fixture of US politics. In January alone, internet bots have opposed Trump critic Mitt Romney’s decision to run as senator for Utah, blamed the government shutdown on congressional Democrats, and are currently backing a campaign to publish a classified memo about bias in the Trump-Russia investigation.

In the last 48 hours, Russia-linked bots tweeted the hashtag #releasethememo 617 times, according to Hamilton 68, a project run by the German Marshall Fund think tank that tracks bots “tied to Russia-linked influence networks.” That’s more than their next five most tweeted hashtags combined.

Fed up with it all, prominent Democratic lawmakers senator Dianne Feinstein and representative Adam Schiff have written to Twitter CEO Jack Dorsey and Facebook CEO Mark Zuckerberg to ask them to investigate. They demanded that the two companies report back by Jan. 26, with answers on how many Russian bots were involved, how many and how often they were posting, and how many accounts were exposed to the campaign.

Part of the letter reads:

We are witnessing an ongoing attack by the Russian government through Kremlin-linked social media actors directly acting to intervene and influence our democratic process. This should be disconcerting to all Americans, but especially your companies as, once again, it appears the vast majority of their efforts are concentrated on your platforms.

Read it in full (pdf).