At one time, if someone entered the US illegally, they were arrested and deported. If they entered on a visa and the visa expired, they could be detained and deported.
However, under the Obama administration, ICE (Immigration and Customs Enforcement) agents are not allowed to detain or arrest illegal aliens for entering the country illegally or for expired visas. The only illegals that can be arrested and deported by ICE agents are those that have been convicted of a criminal offense.
According to Chris Crane, union head of the National ICE Council, an immigration officer can face disciplinary action up to termination for enforcing the immigration laws passed by Congress. ICE agents are being made to be the enemy of the government instead of the upholders of the law.
Crane also explains that under current rules they are being forced to abide by, most of the 9/11 perpetrators would have gone free from arrest and allowed to carry out their plans. Post continues on Last Resistance