WASHINGTON (AP) - Mexicans making short trips across the border who have passed security checks will be allowed to visit the United States for up to 30 days instead of the current three-day limit, government officials said Monday. The change, long sought by Mexicans and border-state politicians, is a gesture that could help President Bush win support in the election battleground states of Arizona and New Mexico. The 30-day limit will be available to Mexicans who hold so-called laser visas, which require background checks and other security measures, Sen. John Cornyn, R-Texas, confirmed Monday. The Homeland Security Department declined comment....