There was no national security letter involved here, and as far as I can tell all parties did follow the law. As far as I can tell, it's actually Twitter's term

There was no national security letter involved here, and as far as I can tell all parties did follow the law. As far as I can tell, it's actually Twitter's terms of service that caused the trouble here, as they deny you ownership of your own content and thus prevented Harris from defending the rights he gave up by tweeting. At any rate, this talk of national security letters sidestepping the law and all that seems quite beside the point. This was just an unfortunate interaction of valid laws and onerous terms of service.