Of course political speech is illegal. Always has been. It just isn’t nominally legal on paper. People have been indicted, prosecuted, and imprisoned for it constantly. A famous example is Eugene Debs, who was prosecuted under the Espionage Act and imprisoned for an anti-war speech he made in 1918.
Please don’t be taken in by the veneer of moronic constitutionalist liberalism. The state punishes people when it feels like punishing people, and does so especially for political speech and dissent…for being an anarchist; for being a leftist. The propaganda it puts down on paper has never changed that.