1. The process by which drugs are generally smuggled into the US from Mexico has been covered by a multitude of news sources for decades. The vast majority are smuggled through border checkpoints; a small minority are smuggled around border walls using tunnels, speedboats, aircraft, etc. It's hard to believe that you've had no exposure to any of this news in the past yourself if you're concerned about border security at all, but even if you hadn't, you could literally have looked this up by typing "HOW ARE DRUGS SMUGGLED INTO THE US" into the search engine of your choice.

2. The more I thought about "how do you know people's motivations for border concerns" question the more I was at a loss to answer it. I didn't say anything about people's motivations; I pointed out that to the extent there is a real migrant crisis on the US-Mexico border, it is a crisis caused by refugees seeking legal asylum, a problem which is entirely orthogonal to any problems that could be solved by a border all, real or virtual. The belief that the United States is treating those refugees inhumanely is also entirely orthogonal to any beliefs about border security, immigration quotas, etc. The "Trump era fight" that I refer to is the fight over the ethics not only of treating refugees this way, but over the honesty -- or, bluntly, lack thereof -- in the way the Trump administration and its supporters have been framing the debate in a way that conflates a refugee crisis with illegal immigration.