Fox News misleadingly invoked the 9-11 terrorist attacks to pillory President Obama's immigration policy, falsely claiming that the hijackers entered the United States illegally, and therefore would not have been arrested had they been detained in 2001 under Obama's immigration policy.

Citing a former Bush Immigration and Customs Enforcement official's February 2012 congressional testimony, Fox & Friends First co-host Ainsely Earhardt claimed that Obama's immigration policy would have allowed the perpetrators of the September 11, 2001 terrorist attacks to remain in the United States had the policy been in effect in 2001, claiming his “policy prevents agents from arresting people solely for entering the country illegally.”

However, the 9-11 hijackers did not enter the country illegally, so any immigration policy changes dealing with people entering the country illegally would not apply. The National Commission on Terrorist Attacks reported that the hijackers entered the United States legally via visas issued by the State Department:

Beginning in 1997, the 19 hijackers submitted 24 applications and received 23 visas. The pilots acquired most of theirs in the year 2000. The other hijackers, with two exceptions, obtained their visas between the fall of 2000 and June 2001. Two of the visas were issued in Berlin, and two were issued in the United Arab Emirates. The rest were issued in Saudi Arabia. One of the pilots, Hani Hanjour, had an application denied in September 2000 for lack of adequate documentation. He then produced more evidence in support of his student visa application, and it was approved.

And while several of the hijackers had overstayed their visas, the Obama administration has taken steps to crack down on those who stay when their visas expire, focusing on security risks. From an Associated Press report in September 2011:

The Obama administration is cracking down on immigrants in the U.S. who have overstayed the terms of their visas by using a system that automatically checks multiple national security, immigration and law enforcement databases at the same time, a senior Homeland Security Department official said.

The common practice has been to make manual checks of individual databases. The new system already has identified dozens of investigative leads, said John Cohen, deputy counterterrorism coordinator at the Homeland Security Department.

The immediate focus is to identify people who have overstayed their visas and who pose potential threats to national security or public safety, Cohen said.

[...]

The department also is checking regularly the systems for people whose visas have not expired -- in some cases, as often as daily or weekly, Cohen said.

Such a review process deals with the reality that information about a person's potential terrorism ties might not be clear to the intelligence community until after a visa has been issued.