Before the Senate Appropriations Committee on Wednesday, Mattis lauded the decision as a way to make managing the war effort more efficient: "This assures the department can facilitate our missions and nimbly align our commitment to the situation on the ground," he said.
Fair enough. But there are -- and should be -- honest concerns about the degree to which the President's hands-off approach to the military provides for a proper set of checks and balances and is healthy for civil-military relations in this country.
For his part, Mattis stressed that the mission in Afghanistan has not changed; it is still one of train, advise and assist. Nor has the number of American troops there today, which stands about 8,400.
It is safe to assume, however, that, eased by this decision, the number could soon increase -- perhaps even before the new war strategy is presented to the President for review and approval, which defense officials now say won't happen for another few weeks.
The current commander of US and NATO troops, Gen. John Nicholson, has made clear he needs several thousand more American troops to help Afghan security forces beat back the advances that ISIS and the Taliban have made in recent months.
Those advances have been real, and they have been lethal.
ISIS now has a branch in Khorasan province, al Qaeda is still present, and according to the special inspector general for Afghanistan reconstruction, the Taliban control about 15% more territory than they did in 2015. Attacks in Kabul during May this year alone killed nearly 100 people.
Mattis himself admitted the United States was not winning the war and that "actions [are] being taken to make certain that we don't pay a price for the delay" in developing the new strategy. There's your signal that troop increases could be right around the corner.
To be sure, Trump's decision to delegate this authority shouldn't come as much of a surprise. He did the same thing not long ago for troop levels in Iraq and Syria, and it is perfectly in keeping with his stated objective of letting "the generals do the fighting, you know."
It's also in keeping with the desires of many military leaders, who bristled at what they considered micromanagement under both the Bush and the Obama administrations. Under Presidents Bush and Obama, troop levels and intra-theater movements were managed by the White House.
These movements, however, involved significantly higher numbers of troops. At the height of operations in Iraq, there were more than 170,000 Americans on the ground. Likewise, by 2010, after President Obama ordered the surge of an additional 30,000 troops to Afghanistan, more than 100,000 Americans were fighting there.
One could argue, then, that Trump's decision "normalizes" what should be the management of lower troop numbers for a mission that is not, and will not, become all-out war again.
But it could also end up absolving him of responsibility.
The American people can be forgiven for wondering whether this new delegation of authority only further encourages our commander in chief to ignore the demands -- the heavy burden -- of wartime leadership and accountability, to obscure from them the logic in decisions that are made about the war in Afghanistan, and, worse, to be able to place himself outside the decision-making arena and blame the generals if/when things go wrong.
This is not a man, let's remember, well known for accepting personal responsibility for his decisions.
"The President has effectively removed himself from decision making, and as the commander in chief he does not get that option," said retired Lt. Gen. Mark Hertling, who commanded troops in Iraq at the height of the surge in 2007, and now works as a CNN military analyst. "He is the only one who can own this. If things don't go well, or it takes too long, does Mattis get the blame?"
There is also the issue of effective policy and strategy making. Neither can be done in a vacuum and both must be informed by the other, as well as by the equities of other agencies -- even other countries.
"Strategy isn't numbers of forces," noted Hertling. "Strategy is what you want to do, the objectives you want to achieve. The forces and the ways you use them contribute to reaching the objective, but the number of forces you deploy don't contribute to a successful strategy by themselves. And the President is the only guy who defines the strategy of the United States."
Doug Lute, who served as US ambassador to NATO and special adviser and deputy national security adviser for Afghanistan and Pakistan to Presidents Bush and Obama, agreed but also stressed consideration of third-order consequences.
"An effective strategy will align the military part with the political part with the diplomatic part with the economic part with the intelligence part," Lute told me. "If Jim Mattis is increasing or decreasing troops, that could have an important impact on what we're telling the Pakistanis, for instance. What's the impact on Iran, Russia, China or India?"
"I'd be a little cautious that delegating one of those elements to one department or agency absent the others runs the risk of the policy falling out of alignment," Lute said. "How does this all stay together?"
That seems to be the very question that at least one former commander of US troops in Afghanistan believes ought to remain paramount. With cuts -- or at the very least a diminished focus on diplomacy and other elements of power -- he told me he believes a whole-of-government approach, combining military and civilian resources, to the war in Afghanistan will remain elusive.
But in this former commander's opinion, an even larger problem looms: civil-military relations in this country. For him, the numbers of troops we send is just as important as making sure the American people feel invested in that and any other decisions made about the war strategy. One way to ensure this rigorous debate occurs is to have it attended by, if not presided over, the nation's elected leaders.
This delegation of authority the President seems to fancy is a "double edged sword that our leaders have not yet fully considered," he said. "Troop-level decisions and delegation of authorities made outside the public view risks a further distancing between those serving in uniform and the American people."
He noted the public fixation over the Russia probe, compared to the relatively little attention paid to the recent deaths of three US soldiers in a "blue-on-green" attack this week, when an Afghan soldier turned his weapon on the Americans.
In the end, Mattis may be right. This new authority may help make fighting the war in Afghanistan more nimble. If so, that's good for our troops, who still serve very much in a dangerous environment. And it is good for our Afghan partners, who continue to lead combat operations, but who also continue to need the expertise and the firepower of US and NATO nations.
The country is fortunate that, in Jim Mattis, there is sobriety. He is a combat-proven leader, steady and thoughtful, who can be counted upon not to abuse the power bestowed upon him.
As Lute told me, "If agility is given to this Pentagon, with this leadership in place, we should have a high degree of confidence it won't be misused. We shouldn't have instant anxiety over this."
And that's good for the American people, too, who give over to the military their precious sons and daughters.
There is no greater, more consequential decision any president makes than to deploy troops in harm's way. Alleviating that burden from his shoulders should not be permitted -- by him, by anyone else in the national security establishment, or by the American people they represent.
So, where does that leave us?
Well, at least for now, the good news is that the Afghan war belongs to Jim Mattis.
The bad news is the Afghan war now belongs to Jim Mattis.