There are two answers, one on border control, the other on weak internal enforcement due to the fact that immigration law is federal, but enforcement is local. It did not matter which political party was in control of the Executive Branch or of Congress.
Between 1990 and 2000 the illegal population grew from 3.5 million to 8.6 million, or by over 5 million. The illegal population peaked in 2007 at 12.2 million. About two thirds of illegal immigrants in the U.S. come from Latin America, and possibly 75% of illegal Latin American immigrants arrived by crossing the Mexican-American border without authorization. These estimates suggest that that during the 1990s, illegal Mexican border crossings into the U.S. were in the range of 250,000 or more a year. Taking into account some out-migration, and the uncertainty of all these estimates, an annual inflow in the 1990s of 250,000 over the Mexican border is conservative.
The pressing question is, Why did immigration control fail in the 1990s, and to such degree that even after 9/11 the borders remained porous? Aside from the pull of employers in the U.S. and the push of Hispanics seeking a better job, why did control of migration fail so miserably, especially after passage of the 1986 Immigration and Reform Control Act, which was supposed to have put the problem of illegal immigrants under control?
Douglass Massey’s writings with co-authors explain why the borders remained leaky even after Washington appears to redouble efforts to improve control. A 1997 presentation by Douglass Massey and Audrey Singer, concluded that “Despite the apparent build-up of enforcement resources along the Mexico-U.S. border and the launching of highly publicized initiatives, the probability of apprehension fell in the late 1980s.”
A federal website relates that “Operation “Hold the Line” was established in 1993 in El Paso, and proved an immediate success. Operation “Gatekeeper” was implemented in 1994, and reduced illegal entries in San Diego by more than 75% over the next few years.” But total figures contradict this sunny assertion.
In the early 1970s, the chances of being caught by border enforcement was 35%-40% per attempt, but by the early 1990s the chances were 15%-20%. At this low risk, the cat-and-mouse game was tilted in favor of the border-crossers, whether with coyotes or unassisted.
Massey and Singer find that the Immigration and Naturalization Services was focused on drug smuggling in the 1990s. That was the decade prison sentencing turned more severe for drug crimes.
Tougher border control did, however, reduce the once fluid circular movement of Hispanics back to south of the border, as persons already in the U.S. became more worried about being able to return north.
In 1998, 278 million people, 86 million cars, and four million trucks and rail cars entered the United States from Mexico. More than half of the cocaine and large quantities of heroin, marijuana, and methamphetamine entered the United States across the border.
The authors wrote in 1997 that “INS efforts to build goodwill and garner political support by joining the popular war on drugs have not noticeably slowed the entry of controlled substances, but they have greatly facilitated the entry of undocumented migrants by shifting scarce enforcement resources away from catching undocumented migrants toward intercepting drug smugglers.” With a lowered capture rate, Hispanic gained more experience in the cat-and-mouse game; success at crossing over led to more success.
A new book, Policing Immigrants, examines the actual practices of state and local police in enforcing federal immigration law far away from the border. There is no federal police force assigned to enforce immigration laws (or any laws, for that matter). How immigrant laws are enforced is subject to a patchwork of policy, legislation and enforcement. “Standards are unclear, and guidelines for enforcing immigration law are changing and often vague,” the authors write. On top of which, the concept of community policing, which places a very high value on trust between local police forces and the community of residents, is extremely hard to square with immigration law enforcement.
It was not until 1997, with the passage of the Illegal Immigration Reform and Immigrant Responsibility Act, that there was statutory support for the federal government to formally authorize local police departments to participate in joint training, planning and application of the laws. The risks of misadventure are high, demonstrated by the Maricopa County, AZ sheriff Joe Arpaio, who raided a city hall without notifying local police in advance, and using a state law aimed at human smugglers to arrest the clients of smugglers.