[tentcamper]

Yes you need a passport to re-enter the USA. I think it was after 911 that they
started. It use to be few questions and you entered the US. I think Canada asks for a passport to confirm you will can re-enter and not be stranded in Canada.

Some of the border states offer driver licenses that have verified passports and if you have one of them. US customs accepts those licenses to come back to the US.