Using data provided by the U.S. Census Bureau, the ACLU has determined that nearly 2/3 of the entire US population (197.4 million people) live within 100 miles of the US land and coastal borders.
The government is assuming extraordinary powers to stop and search individuals within this zone. This is not just about the border: This " Constitution-Free Zone" includes most of the nation's largest metropolitan areas.
My understanding is that they cannot perform a border search when they are not at the border unless its fairly clear that you did cross the border. This ACLU information suggests otherwise but doesn't substantiate that suggestion as far as I can tell.
American Civil Liberties Union : Constitution Free Zone