TIJUANA, Mexico — Tijuana was once known as a red-light district, watering hole and gambling magnet for Southern California. In recent years, it's grown to a city of 1.8 million people with thriving arts, music and culinary scenes — but lately that's been overshadowed by a surge of violence.

Last year, the city just across the southern border saw a Mexico-leading 1,744 homicides, an all-time high, according to the Baja California Attorney General’s Office.

"Dateline" visited Tijuana to explore the impact of that violence and why it had not spread across the U.S. border to San Diego.

While President Donald Trump has repeatedly said that he wants to build a southern border wall to keep crime at bay, the most blood-soaked city in Mexico is sending very little, if any, of its violence to its northern neighbor, experts say.

“It doesn’t bleed over,” says Everard Meade, director of the Trans Border Institute at the University of San Diego. “These two cities are really close, but large segments never cross the border.”

San Diego, the second largest city in California saw only 35 murders in 2017, a 30 percent decrease compared to 2016. The homicide number is reflective of near 40-year lows for murder seen during much of the decade, according to police data.

One reason is that the border region is fortified with hundreds of law enforcers from U.S. Customs and Border Protection, Immigration and Customs Enforcement, the U.S. Drug Enforcement Agency, the FBI, and the U.S. Coast Guard. The FBI has a Cross Border Task Force that has thwarted cartel crime through wiretaps and GPS tracking, said the U.S. Attorney in San Diego, Adam Braverman.