Washington DC - Homeland Security secretary nominee Kristi Noem said Friday weaknesses at the southern border are the country's "number one threat" as she set out her vision for the department that will oversee Donald Trump's promised immigration crackdown.

The South Dakota governor would be in overall charge of Customs and Border Protection and Immigration and Customs Enforcement (ICE) – agencies on the front line of US efforts to address a rise in the number of undocumented migrants entering the country in recent years.

The department also leads on cybersecurity, terrorism, and federal emergency management – another hot-button issue in the wake of last year's two devastating hurricanes and the ongoing wildfires in Los Angeles.

Noem (53) is best known internationally for sinking her chances of being Trump's vice-presidential pick with her cheerful admission that she had shot her dog, Cricket, because it was "untrainable."

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Despite her state's distance from Mexico, Noem sent National Guards troops to the frontier, earning plaudits from the Republican right.

In her opening statement, she said the southern border would be a top priority, asserting America's "responsibility to secure our borders against those who would do us harm" while stressing that the system must be fair and lawful.

Underlining her focus on the issue, she was asked about domestic terrorism but pivoted back to the border.

"This is a grave concern for our country, as we all agree that the number one threat to our homeland security is the southern border," she said.

Undocumented immigration was a key topic in November's election, and Trump's promises to seal the border and carry out the largest deportation program in American history appeared to resonate at the ballot box.

After the election, Trump named as his new "border czar" Tom Homan, a former acting director of ICE who oversaw a policy that separated parents and children at the border.

Noem, who would be his boss, appeared to have robust support from Republicans who are in the Senate majority and will ultimately decide her future.

But the job is considered a pressure cooker, and Trump went through six permanent or acting Homeland Security secretaries during his first term.

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The Democratic appointee that Noem would replace, Alejandro Mayorkas, was a target of Republican fury as undocumented entries across the southern border soared in 2023, and he was impeached last year.

Homeland Security Committee Chairman Rand Paul described the 260,000-employee DHS as an agency that "epitomizes unchecked power" and "demands rigorous scrutiny."

He said Noem would have the task of restoring "transparency and accountability" to a bureaucracy that had "lost its way."

Democrats did not give Noem the hard time that other nominees have experienced, and the opening exchanges were cordial.

"Governor, thank you again for your willingness to serve in this incredibly important position," said Gary Peters, the panel's top Democrat.

While much of the questioning focused on immigration, Noem was asked to address the distribution of disaster aid, with Trump and other Republicans suggesting relief for fire-ravaged California should be conditioned on the actions of the state's Democratic leaders.

"Under my leadership at the Department of Homeland Security, there will be no political bias to how disaster relief is delivered to the American people," she pledged.

Newly released financial disclosures reveal that Noem made $139,750 in an advance payment for the memoir in which she recounted how she shot and killed her disobedient family pet.