Mattis made clear the president does not share his views on alliances and authoritarianism.

Secretary of Defense James Mattis is stepping down from the Trump administration — and he used his letter of resignation to make clear that he’s doing so because of fundamental disagreements with President Donald Trump’s ideas and approach to foreign policy.

In the letter, Mattis describes his core beliefs: that America’s strength is linked to its “alliances and partnerships” abroad, that the US should resolutely resist attempts from China and Russia to “shape a world consistent with their authoritarian model,” and that the US should protect the “international order.”

Then Mattis makes clear that he thinks Trump does not share these beliefs.

“Because you have the right to have a Secretary of Defense whose views are better aligned with yours on these and other subjects,” Mattis writes, “I believe it is right for me to step down from my position. The end date for my tenure is February 28, 2019.”

You can read the full letter, posted on Twitter by ABC’s Elizabeth McLaughlin, below: