Mullin sworn in as DHS chief after GOP fracture forced Dem to save nomination

Mullin, 48, is a former mixed martial arts champion and plumbing business owner who will replace outgoing Secretary Kristi Noem, a South Dakota Republican recently picked to lead the Shield of the Americas security initiative announced by Trump earlier this month.

Mullin was sworn in by Attorney General Pam Bondi as Trump introduced the Oklahoman as a "man who's going to do a phenomenal job for a country."

"I tell you, your family has to be very proud. You have to be very proud. Everybody wanted this job. I said, there's one man for this job and I have no doubt he's going to be fantastic," Trump said.

After Bondi administered his oath, Mullin approached the microphone and said it was the most nervous he's ever been.

"It just seems surreal being in the Oval Office and having the president of the United States speak so highly of me and then recognize my family and know my family by name. It's humbling," he said.

"And, I never take it for granted - but I've made this very clear that I don't care what color your state is. I don't care if you're red or you're blue. At the end of the day, my job is to be secretary of Homeland [Security] and to protect everybody the same. And we will do that. I'll fight every single day."

Mullin said that prior to his swearing-in, he visited with DHS employees including some working without pay due to a Democrat-forced partial shutdown of the agency.

"If you need anything to know their dedication to show up and still protect the homeland that you and I enjoy and the freedoms that we're that we're experiencing, they're working with for free because of political politics. That's all I need to know. I told … I'll be fighting 365 days beside you. No one's going to outwork me. And I'm not going to let any of them outwork me. The president is entrusting me with this, and failure's not an option."

"This is going to surprise some people, but I consider Markwayne Mullin a friend. We have a very honest and constructive working relationship. We have authored legislation together, such as the Tribal Buffalo Management Act, and we crafted the Legislative Branch Appropriations bill together this year," Heinrich said.

"We often disagree and when we do, we work to find whatever common ground we share."

"He's a strong business leader who understands the power of free markets and limited government. He spent his career fighting for Oklahoma's energy industry and providing affordable, reliable energy to all of America," Stitt said of Armstrong on Tuesday.

Former Arizona Gov. Janet Napolitano, former Air Force general counsel Jeh Johnson, Gen. John Kelly (Ret.), and former Deputy Trump White House chief of staff Kirstjen Nielsen also prominently served.