The Obama administration may regret pushing General James Mattis, the brilliant and blunt-talking Marine who is head of Central Command, into retirement for a variety of reasons—not the least of them being that, with his impending retirement looming, he has felt free to voice undiplomatic truths.

In his testimony before the Senate Armed Services Committee on Tuesday, he was asked whether sanctions and diplomacy were preventing Iran from acquiring nuclear arms. His blunt answer: “No, sir” He followed up by explaining: “That should not be in any way construed as we should not try to negotiate. I still support the direction we’re taking. I’m just — I’m paid to take a rather dim view of the Iranians, frankly.” Needless to say his “dim view” is a lot closer to reality than the daydreams of political staffers in the White House who imagine that some kind of diplomatic breakthrough with the mullahs is likely.

When he was asked about how many troops the U.S. should leave behind in Afghanistan after 2014, Mattis replied with equal frankness that his recommendation has been to keep 13,600 U.S. troops on the assumption that NATO would provide half as many, for a total international force of 20,000. That is roughly half the figure that the White House has been floating as a possibility. But, again, Mattis’s assessment is a lot closer to the mark than the politically driven happy-talk from the White House.

No doubt Mattis caused some consternation in the White House by telling the truth about Iran and Afghanistan—the very definition of a “Washington gaffe”—but it is precisely because of his willingness to speak truth to power that Mattis will be so dearly missed. He is one of the few senior governmental appointees left, after the departure of Clinton, Gates, Panetta, and Petraeus, who can inject some reality into a foreign policy that increasingly seems to be dominated by a handful of like-minded presidential cronies.