US Representative Devin Nunes has sued Twitter and a handful of users for defamation and negligence, accusing Twitter of acting as a “vessel of opposition research” for hosting accounts that insulted Nunes. The suit is the latest of several filed against social media platforms for alleged bias against conservative politicians, none of which have made substantial progress in court.

Nunes’ lawsuit mostly focuses on a cluster of Twitter accounts that Nunes claims were coordinating libelous attacks on him, primarily “Devin Nunes’ Cow”, the now-suspended “Devin Nunes’ Mom”, and the account of Republican political consultant Liz Mair. The complaint — published by Fox News this afternoon — quotes numerous tweets from those accounts, which it claims “maliciously attacked every aspect of Nunes’ character, honesty, integrity, ethics, and fitness to perform his duties as a United States Congressman.” The attacks included accusing Nunes of racism, claiming he had obstructed justice in the Congressional probe on Russian political interference, and calling him a “treasonous cowpoke.”

But the suit also claims that Twitter bears legal culpability for the attacks, since it “consciously allowed the defamation of Nunes to continue” by not suspending the accounts. “Twitter did nothing to investigate or review the defamation that appeared in plain view on its platform,” it says. “As part of its agenda to squelch Nunes’ voice, cause him extreme pain and suffering, influence the 2018 Congressional election, and distract, intimidate and interfere with Nunes’ investigation into corruption and Russian involvement in the 2016 Presidential Election, Twitter did absolutely nothing.”

Nunes also accused Twitter of “shadowbanning” his account, referring to an incident in which some Twitter users’ names failed to appear as auto-suggestions. Twitter has previously stated that the issue affected a wide spread of accounts, and that it arose from the design of an automated system, not an intent to demote specific accounts. (It also doesn’t fall under the traditional definition of “shadowbanning,” since the accounts were still accessible through searches and to followers.) A Twitter spokesperson declined comment on Nunes’ lawsuit.

According to Nunes, Twitter’s importance gives it “a duty to exercise ordinary and reasonable care” in policing defamation. “Twitter’s use of its platform as a portal for defamation by political operatives and their clients runs contrary to every tenet of American democracy,” the suit says. “A candidate without Twitter is a losing candidate. The ability to use Twitter is a vital part of modern citizenship,” because “Twitter is not merely a website: it is the modern town square.” He’s requesting $250 million in damages for Twitter’s alleged negligence.

Some courts have held that Twitter is a kind of public square — but in the context of public officials engaging with users, not Twitter allowing people onto the platform. So far, judges have supported web platforms’ right to ban or demote users as they wish, and they’ve avoided holding them responsible for user posts. An appeals court threw out a lawsuit from white nationalist Jared Taylor over a Twitter ban, and an expansive case against Facebook, Google, Twitter, and Apple just suffered a defeat in court. And the California Supreme Court ruled that Yelp couldn’t be required to take down a defamatory user post, a decision that the US Supreme Court left standing in January.

If these tweets are legally defamatory, Nunes’ accusations against Twitter might be stymied by Section 230 of the Communications Decency Act, which holds that web platforms aren’t liable for content that’s posted by users. (We also don’t know if a court would find them defamatory — simply calling someone a racist, for instance, is generally a defensible statement of opinion.) This complaint doesn’t appear to accuse Twitter itself of defamation, but it’s not clear that Nunes’ negligence argument is much stronger, nor that a court is likely to grant his request to make Twitter suspend all the accounts in question.

Regardless of how far this lawsuit progresses, Twitter and other platforms are under fire in Congress, where CEO Jack Dorsey appeared for two hearings last year. Tech companies have every incentive to avoid making legislators angry — even if the courts have been fairly sympathetic.