Close video Trump infidelity to allies drives Mattis to resign in protest Courtney Kube, national security and military reporter for NBC News, talks with Rachel Maddow about the backstory on Gen. Jim Mattis’s resignation as Donald Trump’s secretary of defense, and what it means for U.S. allies and initiatives around the world. Courtney Kube, national security and military reporter for NBC News, talks with Rachel Maddow about the backstory on Gen. Jim Mattis’s resignation as Donald Trump’s secretary of defense, and what it means for U.S. allies and initiatives around the world. share tweet email Embed

When Donald Trump first announced via Twitter yesterday that Defense Secretary James Mattis would “ retire ” in a couple of months, the news hardly came out of the blue. The two disagreed on a great many issues , most notably the president’s decision this week to precipitously withdraw all U.S. military forces from Syria.

But it wasn’t long after the public saw the tweet that Mattis’ resignation letter came to light, and at that point, it quickly became apparent that this wasn’t just the latest cabinet shake-up in Trump World. On the contrary, the retired four-star general made little effort to hide his concerns about the president’s judgment.

In the letter, Mattis suggested Trump was not treating allies with respect and had not been “clear-eyed” about U.S. enemies and competitors. “My views on treating allies with respect and also being clear-eyed about both malign actors and strategic competitors are strongly held and informed by over four decades of immersion in these issues,” he wrote. Mattis told the president in the letter that he should have a defense chief who shares his views.

This was not, in other words, a “retirement.” It was the Pentagon chief – generally seen as the most respected member of this president’s cabinet – declaring, in a public and brutal way, that he could no longer endorse Trump’s agenda by serving in his administration.

At face value, the circumstances may not seem especially extraordinary. After all, much of Trump’s original cabinet is now gone.

But while that’s true, let’s not miss the historic significance of yesterday afternoon’s developments. James Mattis is the first secretary of Defense to ever resign in protest, declaring that the sitting president is not acting in the nation’s interests.

Sen. Chris Murphy (D-Conn.), a member of the Senate Foreign Relations Committee and someone who talked to Rachel on last night’s show, went so far as to write, “A Secretary of Defense quitting over a public disagreement with a President whose foreign policy he believes has gone off the rails is a national security crisis. No way around it.”

Similarly, Leon Panetta, who served as Defense secretary, CIA director, and White House chief of staff for Democratic presidents, told the Washington Post that Mattis’ resignation is a singular moment and that his letter, which underscores how Mattis sees Trump’s approach as misguided, “puts the security of the nation right now at some degree of risk.”

There’s no word yet on whom Trump will tap as Mattis’ successor – if recent history is any guide, Mick Mulvaney might be in contention, since the president turns to him for so many positions – though who’d want the job after seeing the way Trump ignored the retired general for the better part of two years?

Mattis’ tenure is scheduled to end at the end of February. Whether he makes it that long remains to be seen.