Chris Stein, The Guardian:

Donald Trump on Thursday announced he was replacing Kristi Noem as the homeland security secretary, capping weeks of bipartisan complaints about her leadership after immigration agents killed two US citizens and reports emerged that she was involved in a personal relationship with a top deputy.

Noem’s firing was the first major personnel shake-up of Trump’s second term. The president made it public in a post on Truth Social, in which he said Markwayne Mullin, a Republican Oklahoma senator, would take over from Noem starting on 31 March.

Noem, who Trump said “has served us well, and has had numerous and spectacular results (especially on the Border!)”, would become special envoy for “the Shield of the Americas”, a security initiative Trump said he planned to announce over the weekend.

She should count herself lucky; if this were Russia she might have fallen out a fifth floor window.

ABC News:

The president had privately expressed deep frustration over Noem's testimony during a Senate Judiciary Committee hearing on Tuesday, sources with direct knowledge of the conversations said.

The sources said the president was upset by a particular exchange when Louisiana Republican Sen. John Kennedy questioned Noem about a DHS taxpayer-funded $220 million ad campaign. Noem repeatedly suggested the president was aware of the campaign and had signed off on it.

A senior administration official tells ABC News that the president did not sign off.

"Absolutely not," the senior administration official said.

Noem forgot the number one rule of the Trump “Family”: the Boss knows nothing about nothing.