Secretary Mattis reportedly has less influence with the president than ever:

The way these recent presidential decisions on major national security issues have played out, as detailed by current and former White House and defense officials, underscores a significant change in Mattis’s role in recent months. The president is relying less and less on the advice of one of the longest-serving members of his cabinet, the officials said.

The president has tended to defer to Mattis on a few things directly involving the military, but on most other foreign policy questions he has ignored what the Defense Secretary recommends. Mattis was apparently able to talk Trump into ordering a smaller attack on the Syrian government than he would have liked earlier this year, but on most of the biggest decisions Trump has made in the last year he has taken the position favored by his more hard-line advisers and Cabinet officials. Mattis is regrettably successful at keeping U.S. forces engaged in unnecessary wars, but he has no luck when it comes to persuading the president not to make colossal foreign policy errors. The Secretary of Defense is just influential enough to stop Trump from withdrawing troops from a pointless war in Afghanistan, but not nearly influential enough to prevent U.S. withdrawal from the nuclear deal. Unfortunately, supporting the war on Yemen is one policy where Trump and Mattis seem to be fully in agreement, and so the administration continues that completely indefensible support for the Saudis and their allies.

It is not really surprising that Mattis’ influence has diminished in recent months. Since Tillerson and McMaster left, Mattis has no natural allies inside the administration. Meanwhile, their replacements are much more aligned with the president and have done a good job flattering him. The hiring of Bolton over his objections was a sign that Mattis was losing ground. He disagrees so often with Trump that it was just a matter of time before the president stopped listening to him. It is possible that Mattis will hang on as long as he doesn’t contradict Trump publicly, but it seems likely that he will become increasingly irrelevant within the administration as time goes by.