Searching for Conflicting Trademarks
While you are not required to search for conflicting trademarks, it is highly recommended. Should there be any existing trademarks already federally registered that conflict with yours, your application can be denied and your filing fees would not be refundable.
Additionally, since trademarks can be created through common law simply by using them, it is also advisable to search for "common law trademarks" (Those trademarks being used but not federally registered).
You can use a professional trademark search company, such as LegalZoom, to research not only federally registered marks but also common law trademarks.