The US Senate on Monday confirmed Markwayne Mullin to serve as secretary of the Department of Homeland Security, elevating the Republican senator to a role where he will be among the public faces of Donald Trump’s crackdown on undocumented immigrants.

The Republican controlled chamber confirmed Mullin largely along party lines, with a vote of 54-45. Rand Paul of Kentucky was the only Republican to vote against him, while Pennsylvania’s John Fetterman and New Mexico’s Martin Heinrich were the sole Democrats to vote in favor.

While Fetterman endorsed Mullin shortly after his nomination, support from Heinrich was a surprise. After voting to advance his nomination over the weekend, Heinrich released a statement calling Mullin a “friend” who “is not someone who can simply be bullied into changing his views”.

“I look forward to having a secretary who doesn’t take their orders from Stephen Miller,” Heinrich said, referring to the White House official who is an architect of Trump’s immigration policies.

Mullin is set to play a key role in implementing those policies, which polls show are growing increasingly unpopular among the public ahead of the November midterms, in which Republicans will be defending their control of the Senate and House of Representatives.

A former House representative who was elected Oklahoma’s junior senator in 2022, Mullin now leads a 260,000-employee department whose sub-agencies include Immigration and Customs Enforcement (ICE) and the Border Patrol.

Among his first tasks is sure to be stepping up efforts to reopen its operations, parts of which were shuttered in mid-February, when Democrats rejected funding legislation for the department because it did not include new guardrails on immigration enforcement operations.

Democrats demanded the restrictions after immigration agents killed two US citizens during a weeks-long intensive enforcement operation in Minneapolis, and have listed among their demands a ban on officers wearing masks, a requirement that they display identification and adhere to rules on use of force, with all violations investigated.

The shutdown has not impacted ICE or other agencies involved in immigration enforcement, because Republicans authorized tens of billions in dollars of spending for their operations in the One Big Beautiful Bill Act passed last year.

The funding negotiations have grown newly complicated after Trump said no deal should be made with the Democrats until they support the Save America Act, a bill to impose new voter ID requirements that the minority is currently blocking in the Senate. He also deployed ICE agents to some airports to relieve hours-long lines at Transportation Security Administration checkpoints.

At his confirmation hearing last week, Mullin struck a diplomatic tone while signaling he’d take a less public approach to leading DHS compared to his predecessor Kristi Noem, who Trump fired reportedly after becoming dissatisfied with her personal appearances in a series of advertisements for the department.

“My goal in six months is that we’re not in the lead story every single day. My goal is for people to understand we’re out there, we’re protecting them, and we’re working with them,” Mullin told senators.

While he expressed regret for saying Alex Pretti, the second US citizen killed in Minneapolis two months ago, was “a deranged individual that came in to cause maximum damage”, he either deflected questions from Democrats about specific immigration arrests or tactics, or signaled he would not alter course.

Among policies he refused to endorse was keeping immigration agents away from polling stations, where some Trump allies have said they should be deployed, prompting fears that they will scare off voters in the November elections.

“I don’t understand what the concern about enforcing immigration at polling places is anyways. Because, honestly, if you’re not a citizen, you shouldn’t be voting anyways,” Mullin said.

Mullin did, however, affirm that immigration agents would not enter homes or businesses unless they had a judicial warrant signed by a judge. Reports had recently emerged of ICE agents being told that they could enter properties with an administrative warrant, which is an internal document authorized by a supervisor at the agency.

“We will not enter a home or place of business without a judicial warrant unless we’re pursuing the individual that runs into a place of business or a house,” Mullin told senators.

Mullin’s departure from the Senate allows Oklahoma’s Republican governor Kevin Stitt to appoint a replacement, who under state law must be from the same party as the incumbent, and cannot stand in the next election for the seat. The special election to replace Mullin will take place during the midterm elections in November.