WASHINGTON - Confronting a security threat on America's doorstep, President Barack Obama 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 on Thursday, 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 _ never as evident as on Thursday, when the popular U.S. president is sure to stand with Calderon on his own turf and note his courage.

In an interview Wednesday with CNN en Espanol, Obama, indeed, contended that Calderon is doing "an outstanding and heroic job in dealing with what is a big problem right now along the borders with the drug cartels."

As for the U.S. role, Obama said, "We are going to be dealing not only with drug interdiction coming north, but also working on helping to curb the flow of cash and guns going south."

Homeland Security Secretary Janet Napolitano, meantime, said that consultations with Mexico on the drug problem are "not about pointing fingers, it's about solving a problem. What can we do to prevent the flow of guns and cash south that fuel these cartels."

Obama's overnight visit, said senior foreign policy aide Denis McDonough, "is meant to send a signal of respect."

Mexico is the only place Obama is visiting on his way to the two-island Caribbean nation of Trinidad and Tobago for the Summit of the Americas, a gathering of Western Hemisphere nations.

"It will do a great deal in terms of symbolism to raise the profile of the relationship in both cases," said Andrew Selee, director of the Mexico Institute at the Woodrow Wilson International Center for Scholars.

More than 10,000 people have been killed in Mexico in drug-related violence since Calderon's stepped-up effort against the cartels began in 2006. The State Department says contract killings and kidnappings on U.S. soil, carried out by Mexican drug cartels, are on the rise too.

A U.S. military report just five months ago raised the specter of Mexico collapsing into a failed state with its government under siege by gangs and drug cartels. It named only one other country in such a worst-case scenario: Pakistan. The assertion incensed Mexican officials; Obama's team disavowed it.

Indeed, the Obama administration has gone the other direction, showering attention on Mexico.

In words that resounded loudly in both countries, Secretary of State Hillary Rodham Clinton said in Mexico City that the U.S. shared responsibility for the drug war. She said America's "insatiable demand" for illegal drugs fueled the trade and that the U.S. had an "inability" to stop weapons from being smuggled south.

Obama has dispatched hundreds of federal agents, along with high-tech surveillance gear and drug-sniffing dogs, to the Southwest to help Mexico fight drug cartels. He sent Congress a war-spending request that made room for $350 million for security along the U.S.-Mexico border. He added three Mexican organizations to a list of suspected international drug kingpins. He dispatched three Cabinet secretaries to Mexico. And he just named a "border czar."

"This is something that we take very seriously, and we're going to continue to work on diligently," Obama said of the drug violence at a news conference last month. The Justice Department says such Mexican drug trafficking organizations represent the greatest organized crime threat to the United States.

The White House is vowing more enforcement of gun laws. But it is not pursuing a promise Obama made as a candidate: a ban on assault-style weapons.

That ban on military-style guns became law during the Clinton administration in 1994 but expired under the Bush administration in 2004. When Attorney General Eric Holder raised the idea of reinstituting the ban this year, opposition from Democrats and Republicans emerged quickly.

Reopening the debate on gun rights is apparently a fight the White House does not want to take on right now.

"I think that there are other priorities that the president has," Obama spokesman Robert Gibbs said this week.

Mexican leaders, though, say the ban saved lives. "I think it was very good legislation," Calderon told ABC News the day before Obama's arrival.

The swooning economy, blamed largely on failures inside the United States, has taken a huge toll on Mexico. About 80 percent of Mexico's exports _ now in decline _ go to the United States.

Obama and Calderon are likely to tout the value of that trade, but a spat between their countries remains unresolved. Mexico has raised tariffs on nearly 90 American products, a retaliation for a U.S. decision to cancel access to Mexican truckers on U.S. highways despite the terms of a free trade agreement.

On immigration, Obama is expected to make clear he is committed to reforms. The effort is likely to start this year but won't move to the top of his agenda.

A service of the Associated Press(AP)