Are you not aware that in the free world, borders don't work that way. The US border is for keeping undesirables out, which is the responsibility of the US, not for keeping Americans in. The Canadian and Mexican borders are the same, because we are both democracies and relatively free. We don't monitor our borders to make sure Canadians aren't trying to get out of the country for a few days.
And America's drug problem is not a supply problem, it's a demand problem. No country has EVER managed to shut down black markets for what people want. Just look at prohibition -- a complete and total failure -- and in fact in many places increased the amount of alcohol people consumed, only made it more dangerous because it was uncontrolled.
It's time Trump -- and America -- grew up and started to understand how the real world works.