This is a topic that causes frustration because the term "spillover" is used by so many people and agencies with little consistency or agreement. On almost any given day, you can see several government or law enforcement officials on television saying spillover hasn't happened yet, spillover is happening now, or spillover has been happening for years. So which is it?
Well, the problem lies in the fact that there is no single, standardized definition for border violence spillover. Some agencies are looking for spikes in crime levels on the US side that parallel spikes in crime on the Mexican side. Other agencies are basing their assessments of spillover on case information or anecdotal evidence of Mexican DTO-related crimes occurring in US cities, such as targeted killings or kidnappings. Some officials won't call it spillover unless innocent US citizens (i.e. unrelated to the drug trade) on US territory become DTO targets.
First, let's examine the crime statistics angle. One can assume that crime statistics originating from US law enforcement agencies are reliable because agencies on the US side of the border don't suffer from the same corruption issues as Mexican agencies. However, US crime statistics generally don't differentiate between drug-related and non-drug related crimes. It is entirely possible that murders for a US border city could drop from one year to the next, yet the proportion of drug-related murders can rise in the same year. Also, statistics alone don't account for sociological factors occurring in border cities that may skew the meaning of those statistics, such as changes in immigration patterns or economic declines. Finally, crime statistics for cities on the Mexican side of the border are notoriously inaccurate for various reasons, including corruption, lack of reporting, and investigative ineptitude. Mexican crime statistics also do not differentiate between drug-related and non-drug-related crimes.
Next, let's consider case information or anecdotal evidence. We know from publicly available information that the FBI is investigating an increasing number of cross-border kidnapping cases. We also know that hundreds of people in the southwest border states - mostly affiliated with the DTOs in come way - have been kidnapped for ransom or retribution. According to the US Department of Justice, several US-based gangs are affiliated with Mexican DTOs, either distributing drugs for them or contracting themselves out for hits inside the United States. Depending on which source you believe, anywhere from 90-97% of weapons illegally entering Mexico originate in the United States, with most of them coming from the four southwest border states. So does all this criminal activity that seems obviously related to the Mexican drug trade add up to spillover?
Finally, let's take a look at the US-citizens-as-targets issue. There is almost universal agreement among agencies that in almost all cases of border violence, US citizens NOT associated with the Mexican drug trade in any way, shape, or form are NOT being targeted for violence by DTOs or US-based gangs affilated with DTOs. Occasionally, innocent US citizens do get caught in the cross-fire, but usually it's a case of being in the wrong place at the wrong time. Does this mean that spillover is NOT happening?
Ultimately the issue of border violence spillover is a subjective one, and I believe it can't be proven one way or another. I think a strong argument can be made for either position. However the next time you see or hear someone authoritatively trying to say spillover is happening or isn't happening, ask them what their sources are or what proof they have...I'd sure love to see it.