They can't vote in our national elections or decide to live here permanently without permission.
Congress has the power to exercise authority in immigration matters, and immigrants are subject to that authority.
Congress makes immigration law with the approval of the president.
In the wake of September 11, 2001, security issues came to play a central role in deciding who may enter the country, and new legislation took the federal agency tasked with implementing immigration law out of the Department of Justice.
The agency was named the U.S.
The Department of Homeland Security has jurisdiction over Citizenship and Immigration Services.
The United States can't absorb every impoverished or threatened global resident who wants a better or safer life.
It is a political decision to decide who to admit.
When times are tough, nativism, or the belief that the needs of citizens ought to be met before those of immigrants can take on political force, as it did in Donald Trump's campaign in 2016 Jobs are a scarce resource over which political battles are fought.
If times are good and unemployment is low, newcomers may be welcomed with open arms.
Immigration can become an issue when the economy is bad.
Immigrants are big consumers of social services and community resources.
Immigrants do contribute to the economy through their labor and taxes, but because they are distributed disproportionately throughout the population, some areas find their social service systems more burdened than others, and immigration can be a much more controversial issue in places where immigrants settle.
Large numbers of immigrants can change the demographic balance, as we already know that whites will be a minority group by the year 2050.
Being a part of the majority is a source of political power for some people.
When the United States wanted to develop a rocket program, German scientists with the necessary expertise were desirable immigrants.
When our labor force was insufficient for the demands of industrialization and railroad building, immigrants were welcomed.
When our own labor force falls short or is unwilling to work for low wages, immigration law allows for temporary workers to come to work in agriculture.
Our official immigration policy expects immigrants to be skilled and financially stable so that they don't become a burden on the American social services system.
Politics is about how power and resources are distributed in society, and who gets to consume government services is a contentious issue.
Some areas of the country, particularly those near the Mexican-American border, have had serious problems brought on by unregulated immigration.
This is one of the reasons that immigration is a hotbutton issue.
Poor and unskilled residents can overwhelm communities.
Because their children must be educated and they themselves may be entitled to receive social services, they can pose a significant financial burden on those communities.
Some immigrants don't contribute to the tax base because they work off the books.
Most income taxes are federal, and federal money is distributed back to states and localities based on the population count in the census.
Unscrupulous immigrants are reluctant to be counted so their communities are often underfunded.
Many illegal immigrants act like citizens, obeying laws, paying taxes, and sending their children to school.
Some people have lived here for a long time, perhaps because they were children themselves.
The challenge of finding and repatriating them is formidable for those who believe that is the best solution.
It's why many people think giving a path to citizenship is more practical.
Whether motivated by cultural stereotypes, global events, or domestic economic circumstances, Americans have decided at times that we have allowed enough immigrants to settle here, or that we are admitting too many of the "wrong" kind of immigrants.
Immigrants are scapegoated for the nation's problems and demonized as a threat to American culture when this happens.
This happened in the late 1800s and early 1900s with southern and eastern Europeans.
Legislation in the 1920s limited immigration by creating a quota system that favored the northern and western nationalities, seen as more desirable immigrants.
The Immigration and Nationality Act abolished the immigration quota system.
The act doubled the number of people allowed to enter the country, set limits on immigration from the Western Hemisphere, and made it easier for families to join members who had already migrated.
Immigration was hard to control because of more open borders.
The Immigration Reform and Control Act was passed in 1986 in response to the waves of immigrants who entered the country in the 1970s and 1980s.
The law included sanctions for those who hired illegal immigrants, but people continued to cross the border to look for work.
The Immigration Act of 1990 allowed even more immigrants.
The Immigration and Naturalization Service was strengthened in the 1990s under President Bill Clinton.
What's at stake.
On the one hand, there are those who want to wrestle with the issue of the estimated eleven million immigrants already in this country and the demands of American business for the cheap labor that immigrants provide; on the other hand, there are those who want the rule of law to prevail.
Immigration reform, especially the Development, Relief and Education for Alien Minors (DREAM) Act, was one of Barack Obama's top priorities.
Relief would have been granted to young adults who were brought here without documentation.
Obama decided to take executive action because he was unwilling to leave the job unfinished.
In 2012 he announced the Deferred Action for Childhood Arrivals (DACA) policy that allowed children brought in without documentation to apply for a two-year, renewable exemption from deportation during which time they would be eligible for work permits.