It’s happening in part because the American economy, hit so hard by the economic downturn, is finally improving, becoming a draw again for immigrants, especially those from Central America who travel through Mexico on their way to the Texas border. Also, crime remains a terrible problem in many immigrants’ home countries. And word is spreading that the U.S. Congress is contemplating a measure to legalize millions of illegal border-crossers.

That is the backdrop for this week’s Senate debate on border security in the Gang of Eight plan. Democrats are dead set against any proposal that would make permanent legal status and a path to citizenship contingent on measurable improvements in border security. On the other side, many Republicans believe those improvements will never happen unless the law says legalization won’t be allowed without security first. The only question is whether Republicans will stick to their guns or give in to Democrats.

In the debate, supporters of the Gang of Eight bill will almost certainly pronounce the border more secure than it has ever been; such rhetoric is a staple of such debates. But the situation on the border remains troublesome, and if the American economy continues to improve, as everyone hopes it does, the problem could become worse.

Schumer is probably right. In coming years, “lots of millions” will seek to come to the U.S. illegally unless something is done.