How effective are ports of entry in detecting smuggled drugs?

You have to understand that TSA is (at best) a bunch of civilians that took a training course one weekend. They're not the night-vision automatic-rifle wielding CPB narcotics teams tossing flash-bangs through windows or the USCG raiding a container ship in the middle of the ocean.

One thing you have to consider here is that TSA is a fairly young agency under the umbrella of DHS, while CBP and the USCG are their own autonomous agencies. Usually when people talk about these operations, they're talking about the big FBI probe several years back that found TSA doesn't catch a lot of firearms, and other dangerous weapons.

On the other hand, when you're talking about sea ports and drugs (for example), you're talking about maybe a cargo container full of fentanyl which could be worth hundreds of millions of dollars. Usually getting something like that into a port is actually a bit easier than getting it out too, because that requires the complicity of port personnel, or someone authoritative, to accomplish. Sea ports are not generally the sort of place you can walk into and walk out of if you're not supposed to be there, so there may also be logistics companies (knowingly or otherwise) transporting it from the port inland.

If you are talking about legitimate border crossings ("ports of entry"), there was a recent seizure of a tractor trailer packed full of methamphetamine, covered up by just a few boxes of onions. If an entire tractor trailer full of methamphetamine can make it through the border, it can safely be assumed that was a small fraction of it. If there is a market, people will find a way to get that money into their pockets.

If you'd like to look at the stats yourself, they can be found here:

• CPB Air and Marine Operations Statistics
• CBP Enforcement Statistics Fiscal Year 2020 (also has some stats dating back to 2014)

And here are some articles on the topic:

• Meth, cocaine, heroin: Most gets smuggled through ports of entry. A wall won't stop it.
• Want to know where most drugs cross the border? Look at the Border Patrol’s news releases.

A couple of interesting notes:

1. As reported by Washington Post in the last article, "the plurality of those who were arrested for allegedly attempting to smuggle drugs into the United States were identified either explicitly as U.S. citizens or identified as residents of the United States." This means that most of the people found to be smuggling were U.S. citizens or permanent residents.
2. Illicit opioids are fairly rarely seized, according to CPB's own stats. To me that is really troubling, considering the damage they can do in the wrong hands. The vast majority of seizures are cannabis ("marijuana"), followed by illicit stimulants (cocaine then methamphetamine). Comparatively, the fentanyl seized each year was about a hundredth of the weight of seized cocaine. Either they're really good at hiding it, or they're just not trying to find it (see: #3).
3. Corruption is almost a fact of life for some CBP officers (who is, interestingly, one of the only law enforcement agencies that does not require psychological evaluations). If not simple bribery, some have been caught smuggling drugs themselves

Aside/IMO: This is why we really ought to focus on the underlying societal issues that motivate people to seek out illicit drugs and/or simply end their prohibition (which would remove any profit motive from the trade). Law enforcement cannot solve these problems.

I have some reliable first hand knowledge that TSA also gets tested on narcotics and chemical componants of explosives and do fairly better (it helps that they have dogs trained to sniff out narcotics) and the process entails more than just letting the plant walk through security with contraband (the one I'm aware of, the plant had a marked TSA handler with them at all times and they had to escort them at all points behind the security checkpoint for cleared luggage. Since they were training dogs, a person with a bright yellow safety vest with the letters TSA isn't going to tip off the dog that they should look there because like most members of the canine family, TSA dogs can't read. They also don't work with the handler daily, so they aren't going to look near them out of familiarity... the plant will look like a typical passenger and is usually a volunteer from another entire Government agency with a local office to the airport. (so they're reasonably reliable, but have now working experience in TSA or DHS to affect the test. The handler is more there to make sure the contraband isn't stolen from the plant, rather than any distrust of the plant themselves. The plant doesn't have a valid ticket for a flight and they already know where they live because the same boss sighs the checks for them, so it's not like they're gonna get far with illicit goods. They don't want a random passenger picking it up unknowingly... or worse, knowingly.).

Most ports of entry have several layers of checks, both passive and active and both visible and not visible so there's not a full accounting of what they use. While its assumed that the check point and lines for a pre-fight groping are "security theater", its not the only way security stops the bad actors. If anything its an Active Visible security measure. Just because it doesn't reliabley catch contraband doesn't mean it's not doing it's job... the "groping" jokes go a long way to discourage people from even trying funny stuff that is legal, or not paying close attention to the rules... or even oversharing (TSA pre-check lines? Yeah, for a small fee and surrendering information about you that the TSA wouldn't ask for in the normal process nets you a shorter line (when open) and the ability to leave your shoes on for the entire experience. You don't need a warrent if they want to give it to you and ain't no rule that says you can't make some money off the process.).