Stephen Miller has emerged as a top contender to replace Mike Waltz as President Donald Trump’s National Security Advisor, according to a report from Axios.

Miller, who is one of Trump’s top advisors on immigration and the founder of America First Legal, is emerging as a top contender to become the Trump administration’s next National Security Advisor after Waltz was appointed by Trump to become the UN ambassador, five sources familiar with the matter told the outlet.

Miller is the deputy chief of staff in the Trump White House and has played a large role behind the president’s crackdown on illegal immigration. Secretary of State Marco Rubio has temporarily taken over Waltz’s responsibilities as the national security advisor as Trump picks a replacement.

One source with the White House told Axios that Miller has made the Homeland Security Council run “like clockwork” and that the organization is “infinitely more effective than the NSC [National Security Council] with a tiny fraction” of previous staff.

Another source at the White House commented that Miller works well with Rubio on immigration issues and that putting Miller in the role “might be a perfect match,” the outlet reported.

“Given how well he’s worked with Marco, many see him as the perfect person to restore the role of the NSA to a staff-level policy role that reports to the chief of staff, instead of some inflated Cabinet position,” another source told the outlet.

The outlet reported that another individual said Miller signaled he would be interested in the role on Thursday. However, a fifth source told reporters at the outlet he may not take up the role if it takes him away from immigration policy.