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A former San Francisco police chief and vocal supporter of a sanctuary cities policy is on a short list of candidates to become the new chief of the Border Patrol, according to sources.

As police chief, Heather Fong shielded illegal immigrants, including aliens who committed crimes, from deportation. In contrast, it is the job of the U.S. Border Patrol to catch and deport all illegal immigrants, including those with a criminal history.

"If they bring (a police chief) in for political purposes based on the sanctuary cities model, that politicizes the job and I think it completely undermines credibility and morale in the organization," House Committee on Homeland Security Chairman Mike McCaul, R-Texas, told Fox News.

"If you have someone who is advocating for sanctuary cities, that's the opposite side. They welcome these illegal immigrants to stay in the country. And so I think it's at cross-purpose with the mission itself."

Fong, according to Border Patrol, DHS and Capitol Hill sources, is one of several candidates to replace current chief Mike Fischer, who announced his resignation last month.

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    Fong is currently an assistant secretary for state and local law enforcement at the Department of Homeland Security. If tapped, she would be the first outsider to lead the Border Patrol in its 90-year history.

    That decision is up to Customs and Border Protection Commissioner Gil Kerlikowske, who released a statement Monday saying, “"At this time, CBP has not begun the search for the Chief of the U.S. Border Patrol. It is completely false that any individual could be a potential candidate at this time. We are currently preparing the paperwork to begin the process."

    Rank and file agents were surprised she would be considered.

    "The appointment of Heather Fong would prove that the Border Patrol is no longer the enforcement agency that Congress and the American public intended it to be," according to a statement released by Brandon Judd, head of the agents' union.

    "Heather Fong oversaw a sanctuary city, which is directly contrary to our mission. Her appointment would be for political purposes and the trust of the men and woman of the Border Patrol in DHS and CBP leadership would be lost."

    During her five years as the chief of SFPD, Fong refused to cooperate with ICE, telling reporters in November 2008, "We do not cooperate with ICE when they go out for enforcement of immigration violations of the law."

    A few months earlier, she appeared in a public service campaign telling illegal immigrants they're welcome in the city. In promoting San Francisco's sanctuary city policy on TV, radio, posters and brochures in five languages, Fong said illegal immigrants had nothing to fear under her watch. "San Francisco is committed to providing safe access to public services to our communities," she said.

    In a news conference unveiling the campaign, she told reporters, "We do not work on enforcing immigration laws."

    The chief of the Border Patrol position does not require congressional approval. But given the "border security first" mentality among many on Capitol Hill, McCaul said he believes bringing in an outsider could be a hard sell.