Donald Trump says he is replacing Kristi Noem as homeland security secretary

US President Donald Trump has said he is replacing his embattled homeland security secretary Kristi Noem and will nominate in her place Oklahoma Republican Senator Markwayne Mullin.

Mr Trump made the announcement on social media on Thursday, two days after Ms Noem faced a grilling on Capitol Hill from Republican members as well as Democrats.

Mr Trump said he will make Ms Noem a “special envoy for The Shield of the Americas”, a new security initiative that he said would focus on the western hemisphere.

Ms Noem is the first Cabinet secretary to leave during Mr Trump’s second term.

Her departure caps a tumultuous tenure overseeing immigration enforcement tactics that have been met with protests and lawsuits.

The former South Dakota governor has been criticised over the way her department has spent billions of dollars allocated to it by Congress.

Frustrations over her execution of the Republican president’s hard-line immigration agenda — particularly her leadership after the fatal shooting of two US citizens in Minneapolis — as well as her handling of disaster response, paved the way for her downfall.

She faced blistering criticism from Democrats, and some Republicans, in Congress hearings this week over those issues and others.

Aside from immigration, Ms Noem also faced criticism — including from Republicans — over the pace of emergency funding approved through the Federal Emergency Management Agency and for the Trump administration’s response to disasters.

Mr Mullin would need to be confirmed by the Senate but under a federal law governing executive branch vacancies, he would be allowed to serve as an acting homeland security secretary as long as his nomination is formally pending.

Voting in the Senate just after Mr Trump’s announcement, Mr Mullin said he has “no idea” how quickly his nomination will move.

“The president and I are good friends. So we look forward to working closer with the White House, and obviously I’m gonna be over there a lot more,” he said.

Mr Mullin will take over the third-largest department in government that has responsibility for carrying out Mr Trump’s hardline immigration agenda.

Immigration enforcement during the first year of Mr Trump’s administration was largely defined by high-profile, made-for-social-media operations with flashy names, often led by Border Patrol commander Gregory Bovino, who reported directly to Ms Noem.

Ms Noem often went out on those operations, riding along with officers when they went out to make arrests.

But those high-profile operations in places like Los Angeles, Chicago and Minneapolis often led to clashes with activists and protesters that were captured on video and drove opposition to the president’s policies.

That culminated with the shooting deaths in Minneapolis after which Mr Trump shuffled leadership of the operation. The number of officers there was drawn down shortly afterwards.