All politicians lie. Obama was the single best liar and manipulator I've ever seen. The problem that people seem to have with Trump isn't actually that he's a liar, it's that he's a bad liar. And the concept of "lying" is essentially unregulatable, because what constitutes a lie? If a person absolutely believes something, and are wrong, does that make them a liar if they talk about it? Therefore any regulation of perceived lies is based entirely on having irrefutable proof of that person (e.g voice recording, but even this is increasingly useless in the digital age) admitting that they don't believe the **** that they said.So, US has no radicals. Then tell Republicans, quit calling Dems, Radicals. And quit lying in general. Free speech is not freedom to lie. Also private companies are not subject to the Constitution. Twitter is within its rights to ban Trump and anyone else who lies as much as he does.
Also private companies may be subject to freedom of speech laws. It all depends on whether or not the "space" in which they operate can be considered a "public space". I vaguely remember private companies being told that they can't restrict freedom of speech on their property, at one point, in one ruling. Twitter holds a de-facto monopoly on shortform/soundbite social media, and anybody can sign up and start posting freely. Whether or not that constitutes a "public space", I don't know, since very few laws we can draw from ever intended to deal with the digital forums.