With its restrictions on everything from foreign ownership of real estate to the carrying of sidearms by American drug agents assigned there, the government of Mexico has made its touchiness about its sovereignty clear time and again. But when it comes to the sovereignty of the United States of America, Mexican contempt seems to know few limits. The latest example came at 3:15 p.m. Monday (Jan. 23), as yet another standoff between armed Mexicans and American law-enforcement officers took place in Texas at the very spot where a similar standoff transpired Nov. 17. But instead of a fleeing dump truck...