I used passport card coming back from Mexcio by land, no issues. Actually another guy from my client traveled with me with just a license but he easily passed the "american citizen" test with his looks and accent and was let back in. I was at a border town and wanted to go the other side for sight seeing (I know I am an idiot to have done that, didn't know there was a murder that afternoon in the same street we were driving around). The guy with me was telling me it was OK not to go get card from the hotel...I would have dared not do that, couldn't have passed the "looks like an US citizen" test by any means