Sen. Rick Scott, R-Fla., criticized Biden's "open-border policies" and asked Noem how they have affected South Dakota and her communities.

"We certainly have seen the effects in South Dakota that many of your states did. And I would say every state has seen the effects of an open border and the policies that have been under the Biden administration," she said.

Sen. Peters asked Noem what her plan is to address the threat of U.S.-based terrorists.

In her confirmation hearing, Noem alleged that the Cybersecurity and Infrastructure Security Agency, or CISA, "has gotten far off mission."

"The mission of it is to hunt and harden. It's to find those bad actors and help work with local and state infrastructure, critical infrastructure entities, so that they can help them be prepared for such cyberattacks, and that they can make sure that they're hardening their systems to protect them in the future, recognizing the vulnerabilities that they have," Noem said. "This has gotten far off mission."

Noem added that CISA has "stuck their toe and meddled" in misinformation and disinformation.

CISA has long drawn the ire of Trump and his allies. In 2020, the agency worked to secure the nation's election system against cyber threats. The agency's then-director, Christopher Krebs, was outspoken against false claims made by Trump and his allies about election fraud. He was fired by then-President Trump shortly after Election Day that year.

During his first round of questioning, Sen. Gary Peters, D-Mich., asked Noem about whether she is committed "to ensuring, along with the southern border, that the northern border is sufficiently staffed to maintain its security and robust trade between the U.S. and its neighbors."

In her response, Noem said she'd spoken about the northern border with Peters and Sen. Elissa Slotkin, D-Mich., adding, "I think there's been some universal concern from some of the committee members that as we focus on the southern border, and what we're seeing as far as the invasion there and the amount of people crossing, that the northern border would lose focus, but that will not happen."

Noem's remarks come as the president-elect has alleged that fentanyl is flowing into the U.S. through the northern border and has threatened to impose tariffs on Canada, Mexico and China, writing on social media that “this Tariff will remain in effect until such time as Drugs, in particular Fentanyl, and all Illegal Aliens stop this Invasion of our Country!”

In her opening statement, Noem stressed that securing the southern border is a top priority for her if confirmed as homeland security secretary.

"Border security must remain a top priority as a nation. We have the right and the responsibility to secure our borders against those who would do us harm, and we must create a fair and lawful immigration system that is efficient and is effective, and that reflects our values," she said.

Noem said that she would ensure that Border Patrol agents have the tools, resources and support to carry out their mission and said the same is true of the employees at U.S. Immigration and Customs Enforcement who are "responsible for apprehending, detaining and deporting illegal immigrants and getting criminal aliens off of our streets and out of the country."

Noem added that she would also prioritize a "whole-of-government approach" to cybersecurity issues, saying that she would leverage private-public partnerships and "advance cutting edge state-of-the-art technologies to protect our nation's digital landscape."

In his opening remarks, Sen. Gary Peters, D-Mich., the ranking member of the homeland security committee, highlighted the increasing number of "challenges" facing the Department of Homeland Security.

He spoke about the need to secure the southern border, a cornerstone of Trump's policy priorities, but added, "We also know it's well past time to streamline our immigration process."

The ranking member also referred to the recent terrorist attack in New Orleans and the car bombing in Las Vegas, saying that those incidents were a "deadly reminder that terrorism and radicalization remain very real threats to the homeland.”

In closing, Peters highlighted the threat of cyberattacks and thanked Noem for her "willingness to serve," noting that he was looking forward to a "comprehensive discussion" today.

Senate Majority Leader John Thune, R-S.D., said in his statement introducing Noem that she has experience as his state's governor in "managing hard problems."

"She led our state through the pandemic," Thune said, saying that under her leadership, South Dakota became "a magnet for people from other states who were trying to flee or get away from some of the heavy-handed requirements that were imposed in other states around the country."

In his opening statement, Paul said that he hopes the committee works in the new Congress "to restore transparency and accountability to an executive branch that has grown unchecked."

"Gov. Noem, if confirmed, you will lead an agency that has lost its way. Your record as governor of South Dakota and a former member of Congress demonstrates your willingness to make difficult decisions in the face of significant political pressure," Paul said.

"You have the opportunity today to address how your background and vision will translate to leading one of the most critical and scrutinized departments in the federal government," he said.

Noem has no significant experience with homeland security issues, but she has voiced staunch and consistent support for Trump’s hard-line border policies and joined other Republican governors in assisting immigration crackdown efforts along the U.S.-Mexico border. 

The two-term South Dakota governor, who was previously a member of the House of Representatives, has made immigration a key policy priority. She deployed South Dakota National Guard troops to the U.S.-Mexico border three times throughout her term. Most recently, Noem sent troops to Texas to assist with Operation Lone Star, Texas Gov. Greg Abbott’s controversial multibillion-dollar migrant deterrence program.