You can still cross back through the U.S. border with a picture ID and proof of citizenship such as a Birth Certificate, but plan on a little more time to cross as they confirm your status.
Current rules on Passport Travel
The following summarizes information available on the Department of Homeland Security’s website.
LAND AND SEA TRAVEL
U.S. citizens need to present either (a) a passport, passport card (available in spring 2008), or WHTI-compliant document
; or (b) a government-issued photo ID, such as a driver’s license, along with proof of citizenship, such as a birth certificate.
On June 1, 2009, the U.S. government will implement the full requirements of the land and sea phase of WHTI. The proposed rules require most U.S. citizens entering the United States at sea or land ports of entry to have a passport, passport card, or WHTI-compliant document
Note: The passport requirement does NOT apply to U.S. citizens traveling to or returning directly from a U.S. territory.
U.S. PASSPORT AND WHTI COMPLIANT DOCUMENTS:
U.S. Passport: U.S. citizens may present a valid U.S. passport when traveling via air, land or sea between the U.S. and the aforementioned Western Hemisphere countries.
The Passport Card:
Passport card applications are currently being accepted in anticipation of land border travel document requirements. Based on current projections, we expect to begin production of the passport card in June, and be in full production in July. We will provide additional updates as available. Once in production, the passport card it will only be valid for land and sea travel between the U.S. and Canada, Mexico, the Caribbean region, and Bermuda.
WHTI-Compliant Travel Documents for U.S. citizen travel via land or sea, as of January 31, 2008:
Trusted Traveler Cards (NEXUS, SENTRI, or FAST)
State Issued Enhanced Driver’s License (when available)
Enhanced Tribal Cards (when available)
U.S. Military Identification with Military Travel Orders
U.S. Merchant Mariner Document when traveling in conjunction with official maritime business
Native American Tribal Photo Identification Card
Form I-872 American Indian Card
For further information see U.S. Customs and Border protection.
Main government passport info website: