WASHINGTON Confronting a security threat on America's doorstep, President Barack Obama today is venturing into the heart of Mexico. His swift diplomatic mission is meant to show solidarity with a neighbor and to prove that the U.S. is serious about halting the deadly flow of drugs and weapons.

During his stop in Mexico City today, Obama will emphasize cross-border cooperation and probably put a focus on clean energy, but the economic crisis and the bloody drug trade have set the tone.

Among the other touchy points are disagreement over a lapsed U.S. assault weapons ban, a standoff over cross-border trucking and immigration.

The escalating drug war in Mexico is spilling into the United States and onto Obama's lap as a foreign crisis much closer than North Korea or Afghanistan. Mexico is the main hub for cocaine and other drugs entering the U.S.; the United States is the primary source of guns used in Mexico's drug-related killings.

Mexican President Felipe Calderon's aggressive stand against drug cartels has won him the aid of the United States and the prominent political backing of Obama.

By The Associated Press