If there is one idea that has survived the various incarnations of immigration reform, it is this: If unauthorized immigrants in the United States are allowed to stay, they must go to the back of the line.

President Barack Obama has invoked the line. Congressional leaders have referred to the line. Average citizens on multiple sides of the debate have brought up this notion of the line.

What exactly is the line, who is in it and why is it central to the nation’s most substantial effort to change the U.S. immigration system since the 1980s?

The line represents people outside of the United States waiting to immigrate legally through family or employer sponsorship — currently 4.4 million applicants. Lawmakers, researchers and grass-roots activists debate whether the estimated 11 million unauthorized immigrants in this country should have to wait until all current applicants in line are processed to become legal permanent residents, or whether they should follow a new waiting period not tied to the existing immigration queues.

The simplistic portrayals of the current line do not reflect the complex reality of the nation’s immigration system.

That system is a labyrinth beginning with family or employer sponsorship. The majority of the backlog is in the family category because entry is dependent on the applicant’s age, marital status and relationship to the sponsor, country of origin, and whether the sponsor is a citizen or a legal permanent resident.

Annual caps on the number of visas granted further complicate the process, especially for people from countries with hundreds of thousands of applicants.

Those variables mean that some applicants wait a few years to enter the United States, while others wait up to 23 years.

The numbers

More than 482,000 visas were granted last year for all categories of legal immigration. Many of them went to applicants who waited as long ago as 1988, according to the U.S. State Department, which approves or denies visas.

The agency reported that the average wait for a family visa from most countries is eight years. High-volume nations — Mexico, China, India and the Philippines — have the longest waits. For instance, Mexicans are waiting as long as 18 years while people from the Philippines have waited nearly a quarter-century.

This year, under the existing Immigration and Naturalization Act, a maximum of 226,000 family-sponsored visas and 154,000 employment-based visas will be granted. Visas for the immediate relatives of U.S. citizens — spouses, minor/unmarried children and parents — are not limited by any quota.

The proposals

In recent months, policymakers have seemingly preferred that if unauthorized immigrants are allowed to remain in the U.S., they should not gain legal permanent residency until all current visa applicants have been processed.

With no changes to the nation’s current immigration queues, it could take as much as 19 years to clear the backlog, said Muzaffar Chishti, director of the Migration Policy Institute’s office at the New York University School of Law.

Chishti said Congress has several options, including:

• Keeping unauthorized immigrants in a temporary residency status until all existing legal visa applicants have been addressed.

• Opting for a new system with waiting periods not connected to the current immigration lines.

• Shortening wait times by boosting the number of visas issued each year.

Some leading proposals call for unauthorized immigrants to spend three to five years in temporary status — while they register with the government, pay a designated fine, undergo background checks and meet other requirements — before being allowed to apply for a green card. Then they would need to wait for five years before getting the chance to apply for U.S. citizenship, as long as they fulfill additional criteria.

Obama has suggested an overall wait time of eight to 10 years. Others have said the period should be significantly longer, and still others have said the government should offer permanent-resident status but never citizenship to unauthorized immigrants.

The reactions

Chishti said a decades-long wait for the unauthorized to gain legal permanent residency would create a second class of Americans.

“There is a societal interest in not having so many unauthorized people in the middle of society that undermines law and order, undermines integration, undermines economic advancement,” Chishti said. “We’ve decided it’s in society’s interest to legalize these people. Then it makes most sense to have the process be as inclusive as possible and as quickly as possible.”

During the 1986 amnesty program, which legalized about 3 million unauthorized immigrants, the wait time was one year before they were allowed to apply for permanent residency, and then five more years before they could apply for citizenship.

Such a path is opposed by many conservatives, who said no naturalization option — or even permanent residency — should be considered. They emphasize that Washington should focus on further increasing border security and enforcing the nation’s immigration laws before dealing with residency questions for unauthorized immigrants already in the United States.

“This just points out the illogic in the whole concept of rewarding those who have entered or overstayed illegally, and continues to send the message to the outside world that illegal immigration is OK,” said Peter Nunez, a former U.S. attorney in San Diego and spokesman for the San Diegans for Secure Borders Coalition.

He wants Congress to do a better job of enforcing existing immigration rules and requiring all job-seekers to undergo immigration checks. If the unauthorized are allowed to stay, he said, they should receive only the most limited permit that enables them to work but does not provide access to citizenship, government benefits or the right to sponsor family members to the U.S.

Giving the unauthorized a quick path to legality is unfair to people who have been waiting for years to immigrate here, Nunez said. He also said raising the number of visas given out each year would overtax the economy, labor markets and society in general.

Chishti said comparing applicants still living in their native countries to those who have been living and working in the U.S., and who may have children who are U.S. citizens, is not equitable.

“You are comparing apples and oranges,” he said.

For Enrique Morones of San Diego, an immigrant activist and founder of the group Border Angels, the ability for unauthorized immigrants to get into an immigration line would be a huge improvement regardless of how long the wait takes. For all the political talk about access to U.S. citizenship, he added, he has never been asked by a migrant about naturalization.

“All they want is to be documented. As for getting in a line for residency and then citizenship, the end of a long line is OK,” Morones said. “Currently there is no line.”