This is about Twitter trying to pick winners and losers in the marketplace of attention. I don't think the Feds will have to dig very deep to find a cause for action. Twitter has conceivably already crossed the line to become a publisher. If they collude with other publishers they're running into the territory of anti-competitive agreements. Anti-trust action may be viable. Picking winners and losers and colluding with competitors is in the scope of illegal business. Double down with lobbying violations if the "fact-checkers" are unregistered foreign agents.