Are Maine residents required to show a passport for domestic travel?

For right now, no, you are fine with a driver's license.

If your driver's license has the star in the corner you are good to go. If it doesn't you will need to get a new one issued with REAL ID before October of 2020.

No

Not at the present time only overseas travel there is a deadline for updating liscense to tsa standard though check with bvm

Photo ID...but I like to use my passport