Jiro is right; I am just 2.5 to 3 hours away from where the border is, I am speaking from my experience, I have been there many times and might be move to the bordertown on the American soil.
I've been ask by the ICE agents that where I got the passport, you'll get some random questions when you're up at their booth inspection station. If he/she find you suspicious, doesn't answer to his/her question directly or keeps miscommunicate, you'll have go to the Inspection Area and let them to inspect your vehicle and you will get the questionnaire from the ICE. It has been done to me twice due to the agents who talk too fast for my lipreading skill. So, are they doing their job? Obviously yes. Are the national at stake? Probably but it's difficult to secure the 1,500 miles of the Mexico/US border and more expensive.
I've been ask by the ICE agents that where I got the passport, you'll get some random questions when you're up at their booth inspection station. If he/she find you suspicious, doesn't answer to his/her question directly or keeps miscommunicate, you'll have go to the Inspection Area and let them to inspect your vehicle and you will get the questionnaire from the ICE. It has been done to me twice due to the agents who talk too fast for my lipreading skill. So, are they doing their job? Obviously yes. Are the national at stake? Probably but it's difficult to secure the 1,500 miles of the Mexico/US border and more expensive.