TIJUANA, Mexico — Never a particularly pretty place, the border is at its ugliest right now, with violence, tensions and temperatures all on high.

Once thought of by Americans as just a naughty playland, the divide between the United States and Mexico is now most associated with the awful things that happen here. In towns from the Pacific to the Gulf of Mexico, drug gangs brutalize each other, tourists risk getting caught in the cross-fire, and Mexican laborers crossing the desert northward brave both the bullets and the heat. Last week, a federal judge in Arizona blocked portions of new far-reaching immigration restrictions that she said went way too far in ousting Mexicans. Meanwhile, National Guard troops are preparing to fill in as border sentries.

All these developments are unfolding in what used to be a meeting place between two countries, a zone of escape where cultures merged, albeit often amid copious amounts of tequila. The potential casualties at the border now include a way of life, generations old, well-documented but decaying by the day.