The Passport requirement will not be in effect until next year, presently you only need a Passport if you enter the US from Mexico by air plane, also Canada. We get our news from El Paso TV stations and they covered this a lot.
If walking or driving over and of course coming back across, no problems yet. Coming back will be the problem once it goes into effect. We will be getting ours, not for Mexico, but for Canada. I have heard earlier on something about another less expensive card one could use at the bridges or port of entries. About the size of a credit card, not sure what was called, hadn't heard it mentioned this year. May or may not be around still. Someone at a bridge might know details about it, can't remember where they were to be gotten, not post office like the passports it seems.
Native of Harlingen, Texas