Sadly these agents can be as pure as the driven snow and have the greatest love of America but all it would take is the drug cartel grabbing Cousin Pedro off the streets and telling the agent what he or she must do to see Pedro alive again. They are vulnerable to this sort of pressure no matter how virtuous they are. And their families members on both sides of the border are also vulnerable to be snatched or threatened. If you want affirnative action, assign them to the Canadian border and assign northerners to police the Mexican border.
A return to the traditional American policies of the first one hundred and so years of this Republic would solve much.Legalize and tax all drugs with the provision clearly spelled out that intoxication of any form will not excuse the user from responsibility for his or her actions.Make it perfectly clear than many jobs will require continuation of drug-free testing and those who wish to use certain substances voluntarily restrict their employment options.
Prohibition didn't work in the 1920s and hasn't worked in the last 30 years either.
Those who stand to lose by legalization are the drug and dope gangs,pushers,and the statist control freaks.