Crossing by land one can still use a photo ID plus proof of citizenship (birth certificate or naturalization papers) but I think they are now requiring passports or passport cards for air crossings to re-enter the US.

There's some variability at the land borders - some have been demanding passports for years, while others seem less stringent. We drive a car with Washington plates, live near the border, look & sound "American" and have a plausible story (forgot my birth certificate that day), they have usually let us back in the states with a "reminder". Now I routinely carry my passport.

Point Roberts, Washington is a part of the US that is a peninsula which borders British Columbia at its northern edge. Kids who live there have to cross both borders twice daily to attend school in the US. You can imagine all the challenges that poses.