USA Today reports that order security continues to be a sticking point in negotiations over comprehensive immigration reform. In late March, John McCain insisted that the country needs more enforcement to “assure the American people that we have effective control of the border.” In a recent hearing, GOP Rep. Candice Miller — chair of a key House committee focused on border security — said: “If we do not as a nation have a high degree of confidence that we are securing our border…I think this whole comprehensive immigration reform is going to be a very difficult lift.”

The problem with this requirement — almost unanimously voiced by Republicans — is that it’s hard to know what, if anything, would satisfy their demand.

Last year the Obama administration spent $18 billion on border security and immigration enforcement, a significant increase over previous years. And those funds have gone towards deportations and border surveillance. In 2012 alone, the administration removed 409,849 unauthorized immigrants from the United States, a record number. Overall, in his four years in office, Obama has deported nearly 1.5 million people at a pace of 400,000 per year, far exceeding the number of deportations under previous presidents.

This policy of strict immigration enforcement has brought results. The Government Accounting Office has found that 81 percent of the border with Mexico meets one of three top levels of security, as defined by the Department of Homeland Security. Actual unauthorized immigration has slowed to a halt, thanks to a stagnant economy in the United States and a growing one in Mexico. As the New York Times notes this morning: “the established cross-border networks of family connections that made possible one of the greatest immigration waves in American history are either tapped out — with most close relatives already in the United States — or they are sending people home.”

There’s a strong case to be made that we’ve already achieved the goal of tighter border security. Which raises the question: Why do Republicans insist on even tighter layers of security? It might have something to do with the fact that a critical portion of their base opposes the main immigration proposal on the table: A comprehensive bill with a path to citizenship. Republicans have tried to get around this by demanding ever more concessions from Democrats on border security, in hopes of placating that base. But in the real world, there aren’t many more concessions that can be made. And it’s not clear whether there’s anything that could get the base to accept citizenship.

The bottom line is that Republicans need to give up on winning over the base, and except the consequences of passing a bill. Otherwise we’re not getting reform.

Jamelle Bouie is a staff writer at The American Prospect, where he writes a blog.