Do I need a passport to stop in Honolulu?

Hello im active duty military stationed in Guam. Guam is a US Territory so everywhere I look says I do not need a passport to travel from Guam to the states. But United airlines keeps telling me I need a passport since my flight goes from Guam, to Honolulu, to Denver, to Charolette. Some people I ask say I do not need one and some people say I do. Just seeing if anyone here knows for sure. I don’t have a passport because I travelled to Guam on military orders, but my flight to the states is in about 5 weeks so I’m trying to get a passport asap just in case.