Does an American citizen need a passport to travel into tijuana Mexico for 1 day?

* CURRENTLY:

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. * LATER:

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. source: http://travel.state.gov/travel/cbpmc/cbpmc_2223.html