The investigation of the mass shooting in San Bernardino, California, was just hours old when lawmakers, law enforcement and the public started asking the same question: How did U.S. authorities miss the signs that a Pakistani woman asking for a visa because she was engaged to an American had been radicalized?

Tashfeen Malik came to the U.S. on a K-1 fiance visa in July 2014 and passed multiple background checks and at least two in-person interviews, one in Pakistan and another after she married Syed Farook. Nonetheless, as the shooting attack that killed 14 people unfolded a pledge of allegiance for Malik and Farook to the leader of the Islamic State group was posted on a Facebook page she maintained. The page was under an alias and the pledge went undiscovered for a day.

Members of the House Oversight Committee are set to press administration officials Thursday morning on what safeguards are in place to ensure that would-be extremists are not exploiting a variety of legal paths to travel to the United States.

At issue is how closely the U.S. government examines the background of people asking to come to the country, including reviews of their social media postings.

In remarks prepared for delivery Thursday, committee chairman Jason Chaffetz, R-Utah, said: "It is unclear how someone who so openly discussed her hatred of our country and way of life could easily pass three background checks. We need to understand how the breakdown happened with Malik and what we are doing to make sure it doesn't happen again."

FBI Director James Comey said Wednesday that Malik and Farook communicated privately online about jihad and martyrdom before they married.

Homeland Security Secretary Jeh Johnson said reports of DHS officials being barred from reviewing public social media postings of people seeking to come to the U.S. legally "would not be accurate." DHS launched pilot programs specifically aimed at reviewing social media postings as part of the immigration vetting process, he said.

Both DHS and the State Department also are reviewing the process for vetting visa applications, including the K-1 program, and have been directed by the White House to create specific recommendations for improvements.

DHS is specifically reviewing policies on when authorities at U.S. Citizenship and Immigration Services can look at social media posts as part of the process for evaluating applications for certain visas.

"There are some legal limits to what we can do," Johnson said Wednesday. He added that he thinks reviews of social media should be used more often, but did not provide specifics.

Lawmakers have also pressed for changes to the Visa Waiver Program, which allows many citizens from 38 countries to travel to the United States without being subjected to the in-person interview required to receive a visa. Many fear that foreign fighters who carry western passports will be able to exploit that system to travel freely to the United States.

Earlier this month the House voted overwhelmingly to tighten controls on that program and require visas for anyone who has been to Iraq or Syria in the last five years. Security changes to the program were also included in the Senate version of a massive spending bill expected to be approved later this week.

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