Can a California lawyer practice Federal Law in any state without taking the bar?

No. A California lawyer can practice federal law, but only in the jurisdictions where they are licensed to practice. Simply being a member of the California Bar does not grant them the authority to practice federal law in any other state. They would need to be admitted to the bar of the state in question to practice law there, even if the legal matter concerns federal law. Federal courts generally require lawyers appearing before them to be admitted to the bar of the state in which the court sits.