I agree that the Constitution seems rather simple, but it's the application that gets a bit sticky. The best educated people have been arguing about it for well over 200 years. .
Simple means survival on a battlefield, any century - and we have been invaded! If the military was home where it is supposed to be, and not flung across the NEW Roman empire, then they could do their job, and protect our borders, and not some fort on the proposed pipeline route in Afghanistan!
People coming across the border to pick your tomatoes and clean your toilets is hardly an "invasion." If you want a simple solution to illegal immigration, prosecute the people hiring them and they won't come. Your bio says you're from N. Ga. If you live near Dalton, it's your own neighbors who run the carpet factories who invite them here by hiring them. As far as the military in the Middle East, I agree. .