Does the president's announced policy on Afghanistan make sense? To decide, let's look at how a national security professional would deconstruct Trump's Aug. 21 speech.

A serious national security assessment starts by reviewing what interests you're trying to protect. It doesn't necessarily start with what's already been spent and how many lives have been sacrificed. In the brutal calculus of war and peace, those are sunk costs. Lives lost can be honored. They don't come back.

Also, security spent is like insurance. Once it stops, the coverage stops. The real question is, how much more is country willing to sacrifice? The answer depends what the sacrifice is for.

The U.S. has two critical interests in Afghanistan. One is that the country not become a source of instability in South Asia. President Obama left the Middle East on fire. There is blood running in the streets of Europe. There is a madman in charge in Pyongyang. The last problem the U.S. needs is another important part of the world melting down. And a failed state in Afghanistan could be a big problem.

The second U.S. interest is keeping the country from becoming a playground for transnational terrorists. It is unthinkable to let Afghanistan become again a staging area for transnational terrorism in the manner it was for the attacks on 9/11 (where the U.S. lost in one day more lives and almost as much treasure as we spent in Afghanistan over 16 years).

Neither of these interests can be met by walking away. The U.S. tried that in Iraq. When we pulled support in 2011, ISIS rushed into fill the vacuum against a country not yet strong enough to hold them back. In the aftermath, more lives were lost. Far more money was spent. Even now, Europe still struggles with the aftermath of the caliphate spilling over most of the continent.

So the endgame is not to rebuild the Afghan nation (though we wish the Afghans well). It's not to turn country into a democracy or the land of milk and honey. It's to do enough to keep the country from again becoming a problem for us. That's the definition of victory in this war.

So how does that get done? A strategy requires ends, ways and means. What needs to be done. How will it be done. And what will it be done with.

The goal here is to have an Afghan government competent and inclusive enough to keep the country together with a military capable enough to hold the back Taliban and allow for counterterrorism operations to hunt down al-Qaida, ISIS and the other terrorist groups we worry about.

When it comes to ways and means, the president talked about ensuring enough troops in the right place, with the right rules of engagement to help keep the Afghan military an effective fighting force. This is called the "train and assist" mission. Wisely, the president assigned the task of getting that right to the military, rather than micromanaging the effort from the Oval Office.

The president also talked about holding the Afghan government accountable, pressuring Pakistan to choke off terrorist safe havens, and working with India and European allies to help carry the load.

Having a plan, however, is not enough. Both Bush and Obama had plans for Afghanistan, yet neither proved very effective. A good strategy has to pass the suitable, feasible and acceptable test. Is the strategy suitable? If executed, will it achieve its goals? Given the limited objectives Trump outlined, the answer is yes.

Is the strategy feasible? Are the resources there to do this? Again. Yes.

Is the strategy acceptable? Will the people support it? It has been argued that Americans are war weary. That is wrong. Americans never get tired of being defended or supporting the fight for their vital interests. Americans are failure weary. They were angry about failures in Iraq. They are frustrated at the thought of losing ground in Afghanistan. Americans will support the president if the White House delivers results.

Walking through the strategy from top to bottom, there is a lot to recommend what the president proposes to do. When the politics and the craziness of Washington internecine partisan warfare are stripped away, there is case to be made that Trump has a real plan to fight and win a real war.