"Last year, net immigration from Mexico was zero -- as many immigrants (legal and illegal) left the United States as came here. The flow of illegal immigrants has plummeted in the last few years -- ...."
Respectfully you must be mistaken.
" Border Patrol officials estimate that apprehensions are a good proxy for illegal crossings, so when the numbers go up, it means that the flow of illegal immigrants is going up as well.
Last year’s increase marks a reversal.
Glenn Spencer, head of American Border Patrol, ..said according to their own estimates, the Border Patrol only catches about 30 percent of illegal crossers.."