If I were to only register/trademark my name (for my clothing company) in California and say someone decides to start a clothing company in Texas and files for a FEDERAL trademark of the same name- do I have the right to sue? OR would a federal trademark even be issued to that person? (seems to me like it would be a "likelihood for confusion")
This sounds a lot like the (infamous) Zazu case. If the federal trademark issues, you will likely be restricted to use in the state of California, while the other party would have rights throughout the rest of the country.
If this is a real issue, you should speak with a trademark attorney in California and get a solid opinion.
Your state registration would precede the Federal registration and protect you in California. It could also be used to prevent your competition from coming into California. If you have made sales across state lines (or through the internet across state lines) then you could claim prior use and likely oppose the registration of the Texas company. You can sue based on likelihood of confusion in the marketplace if you had plans to go into Texas or if they try to come into California. All very fact specific.
Q: " ... do I have the right to sue?"
R: You have no cause to sue a person simply for filing a trademark registration application. You can, however, file an "opposition" proceeding with the Trademark Trial and Appeal Board ["TTAB"] to prevent that person's application from maturing into a registration. Your own trademark attorney will explain that process -- and will very likely reach out to the person beforehand to try to resolve the matter amicably.
You can file a trademark infringement lawsuit against the person, however, if the person is actually selling his or her similarly-branded clothes within the same geographic area where you sell your clothes. And no, just because you both sell via the internet does not mean that you both sell in the same geographic area. As my colleagues note, the person who USES a trademark first is its "senior user" -- even if someone else federally registers that mark first. In that case, the registration can be cancelled in a "cancellation" proceeding with the TTAB. But, again, just because you're the senior user does NOT mean that you have cause to sue the "junior user." The principal goal of trademark infringement law is prevent consumers from falsely believing that Company A's product is made by Company B. But that confusion can only occur if the consumers are exposed to BOTH companies' products. So if Company A only sells in the West Coast states and Company B sells only on the East Coast then there's [very likely] no overlap of consumers and so no likelihood of confusion.
Forget who registered what first. Lay out all the facts for your own trademark attorney and then figure out how to proceed. Good luck.
When examining new Federal trademark applications, the USPTO only checks for similar Federal trademark applications and registrations, not state trademarks. It is your job as the senior trademark owner to police the situation and oppose the Federal application before it is registered, or file a cancellation proceeding if the other mark has already registered.