Is Coinbase illegal in the US?

Could you please clarify the legality of Coinbase in the United States? I've heard conflicting information about whether or not it's legal to use this cryptocurrency exchange platform. Some say it's fully compliant with US regulations, while others raise concerns about potential legal issues. As a professional practitioner in the field of cryptocurrency and finance, I'd appreciate your expert opinion on this matter. Specifically, are there any laws or regulations that prohibit or limit the use of Coinbase in the US? And if so, what are the potential risks and consequences for those who use it?