Those increases have been supplemented by other initiatives. In 2006, Bush signed the Secure Fence Act, which authorized 700 miles of fencing – as well as infrastructure such as vehicle barriers, roads, and checkpoints – along the 2,000-mile border with Mexico. The same year, the Bush administration endorsed plans for a "virtual fence" of surveillance equipment to run almost the entire length of the border.
The Secure Fence Act aimed to achieve "operational control" over the entire border, defining the phrase as "the prevention of all unlawful entries into the United States, including entries by terrorists, other unlawful aliens, instruments of terrorism, narcotics, and other contraband."
That, experts say, was an unrealistic expectation. There will never be a secure border by that definition, says Donald Kerwin, executive director at the Center for Migration Studies, which defends migrants' rights.
Even the Berlin Wall failed by that measure, he notes. "At that point they were shooting at unauthorized crossers," he says. "Even on a heavily fortified, militarized 37-mile wall, people were crossing. To think that nobody will cross illegally over a 2,000-mile border is fanciful."
In 2010, that realization – together with rising costs and technological challenges – led the Obama administration to kill the virtual fence.
That doesn't mean the border surge was a failure, though.