You really believe that if this had happened in a city and an armed gang attacked cops who just seized a truck full of drugs the cops would just stand down and watch the gang tow it away? I don't believe it. Even if they were outgunned they'd be shooting the whole time while calling for backup. A situation like this is about more than "dope". It's about whether criminals rule, or the law rules.
It's the border and we all know who rules and who allows them to rule.
Don't confuse am American city with the border. There is no comparison.