-- A look at how Congress has dealt with immigration in the past 25 years:
1986: The Immigration Reform and Control Act of 1986 both tightens controls on illegal immigration and extends amnesty for many undocumented immigrants. It requires that employers attest to employees' immigration status and make it illegal to hire or recruit undocumented immigrants. It also grants amnesty to some seasonal agricultural workers and to undocumented immigrants who entered the United States prior to 1982 and have lived in the country continuously.
1990: The Immigration Act of 1990 created a lottery program that randomly assigned a number of visas, and increased the number of immigrants allowed into the country each year. The law also included exceptions for the English-language portion of the naturalization test.
1996: Under President Bill Clinton, several pieces of legislation are enacted that crack down on various facets of immigration. Specifically, there is a sharp increase in the categories of criminal activity for which immigrants, including permanent residents, can be deported. The laws also impose mandatory detention for certain types of deportation cases, and as a result deportation rates skyrocket.
Sept. 11, 2001: Terrorists attack New York and Washington, D.C., killing nearly 3,000 people. The events put immigration under a microscope because the attackers were foreigners, and change the way many politicians and Americans view immigration. Former Mexican President Vicente Fox goes so far as to say that if it were not for the attacks, Congress would have passed reform legislation that benefited Mexican emigration to America.
2003: The Supreme Court upholds mandatory detention regardless of flight risk for any immigrant offender, even permanent residents.
2005: In 2005 and 2006, Congress holds field hearings on immigration and border security across the country. The Senate introduces a significant bipartisan effort to create a path for legalization for many undocumented immigrants.
December 2005: The House passes a bill criminalizing undocumented immigrants, sparking massive pro-immigrant protests nationwide. The Senate refuses to take it up.
May 2006: Instead of the House bill, the Senate passes a tougher version of a bill crafted by Sens. John McCain, R-Arizona, and Ted Kennedy, D-Mass., which includes a path to legal residency for many undocumented immigrants.
October 2006: The fiscal year 2007 budget boosts funding for Immigration and Customs Enforcement by more than 20 percent, about $1 billion more than President George Bush requested, mostly for detention and transport of immigrants.
November 2008: President Barack Obama is elected, and Democrats sweep both chambers of Congress, giving hope that a major immigration reform bill will be enacted. Obama had signaled interest in reform that included enhanced border enforcement, crackdowns on people who overstay their visa and employers who hire undocumented immigrants and a path to citizenship for some undocumented immigrants.
2009: A comprehensive immigration reform bill introduced in the House fails despite efforts by the Obama administration to get it traction.
April 2010: Saying the Congress had failed to enforce U.S. immigration laws, Arizona passes a law to crack down on various facets of undocumented immigration. Most controversial is that the law directs police to ask for immigration papers from anyone they stop or arrest who they suspect may be in the country illegally.
December 2010: The so-called Dream Act, which would allow undocumented immigrant students a path to citizenship, passes the House in the lame duck session. The Senate GOP filibusters, effectively killing the bill.
April 2012: The Supreme Court takes up the Arizona law. While a decision isn't expected until June, during initial arguments the justices appear to have little issue with provisions requiring police to check the legal status of people they stop for other reasons.