Yes, a domain name can be a trademark, but only if it functions as a brand identifier for a product or service. Merely reserving or registering a domain name with a registrar is not enough to establish trademark rights. To qualify as a trademark, it must be used as something more than just a web address. It must be used in commerce to identify the source of a product or service and to distinguish it from others. BOOKING.COM is an example of a domain name that also functions as a trademark.
A top-level domain name (TLD) is not likely to be protectable as a trademark because consumers are likely to view them as being merely part of a website’s URL, not as an identifier of the particular source of a product or service. Thus, the USPTO refused trademark registration for .sucks.